Overhaul of CMake package and compression libraries

PNGwriter: Add Spack Package

libSplash: Add Spack Package

@adamjstewart
```
think you'll find that if you try running something like:
spack spec libsplash ^hdf5@1.8.15
It will complain that libsplash does not depend on hdf5.
This is a bug in Spack's dependency resolution. A workaround
for this is to tell it to always depend on hdf5.
```

@davydden
```
to expand on @adamjstewart comment, spack will make a union
of dependencies,
i.e. hdf5@1.8.6: + hdf5+mpi = hdf5:1.8.6:+mpi, that's why it works.
```

thank you for the hint!

Adds a package for
[PNGwriter](https://github.com/pngwriter/pngwriter/),
a simple high-level C++ png API used in scientific projects.

```
PNGwriter is a very easy to use open source graphics library that
uses PNG as its output format. The interface has been designed to be
as simple and intuitive as possible. It supports plotting and reading
pixels in the RGB (red, green, blue), HSV (hue, saturation,
value/brightness) and CMYK (cyan, magenta, yellow, black) colour
spaces, basic shapes, scaling, bilinear interpolation, full TrueType
antialiased and rotated text support, bezier curves, opening existing
PNG images and more.
```

PNGwriter is a dependency for [PIConGPU](http://picongpu.hzdr.de),
an open-source, many-core, fully-relativistic particle-in-cell code
and further software developed at
[Helmholz-Zentrum Dresden - Rossendorf](https://www.hzdr.de).

Adds a package for
[libSplash](https://github.com/ComputationalRadiationPhysics/libSplash),
a high-level library around serial and parallel HDF5 for regular
grids and particle data sets.

```
libSplash aims at developing a HDF5-based I/O library for HPC
simulations. It is created as an easy-to-use frontend for the
standard HDF5 library with support for MPI processes in a cluster
environment. While the standard HDF5 library provides detailed
low-level control, libSplash simplifies tasks commonly found in
large-scale HPC simulations, such as iter- ative computations
and MPI distributed processes.
```

libSplash is a dependency for [PIConGPU](http://picongpu.hzdr.de),
an open-source, many-core, fully-relativistic particle-in-cell
code and further software developed at
[Helmholz-Zentrum Dresden - Rossendorf](https://www.hzdr.de).

libSplash builds in two versions, one without MPI writing
domain-decomposed posix-style HDF5 files per process and one
(default) with MPI and MPI-I/O ("parallel HDF5") support
aggregating into a single file per MPI communicator.

libSplash is used in conjunction with
[openPMD](http://openPMD.org), see also
[github.com/openPMD/](https://github.com/openPMD/).

- extra steps in Makefile are ignored by readthedocs

Update ADIOS Package

- remove space before comma
- enable parallel build again (seems to work)

- ADIOS is mainly a parallel I/O library
- a Fortran compiler is non-standard in a minimal install

- always use `mxml` as an external dependency in spack
- declare `build`-only dependencies correctly

Suggest setuptools when creating Python package

Add all Sphinx dependencies

This PR updates the ADIOS package.

**Changes:**

- add latest stable release `1.10.0`
- add previous versions (hashes)
- add default license header
- add build options (shamelessly taken from HDF5 package)
- add validation for excisting FC (as in HDF5) and make optional
- handle mxml dependency correctly (not required in 1.10.0+)
- add `CFLAGS=-fPIC` to build shared (python) libs in ADIOS' lib
- remove `-DMPICH_IGNORE_CXX_SEEK` since it is normally not required
- remove `MPICC/CXX?FC` since `--with-mpi` just performs well
- add transforms:
  - `zlib`: useful (optional) default
  - `szip`: optional (compile often broken)
- add transports that are not as performant as the `.bp` format:
  - `hdf5`: non-default
  - `netcdf`: non-default, close #1610

nwchem: use basename for CC and FC

ape octopus: in-code comments

Matplotlib Python package overhaul

The download tarball for qthreads vanished. Install it from a git branch instead as temporary work-around.

* opencoarrays: new package

* opencoarrays: remove tests from install due to (unimportant) failures in some configurations

* opencoarrays: fix flake8 errors

* Update Julia to 0.5 release branch; install some Julia package as well

* Add comments, correct flake8 error

* Correct flake8 error