I usually want to look at the Travis CI output, but I currently have to
scroll down to see it. This renames checks to be a bit shorter and more
consistent with Travis's naming, and also so that actions appear lower
than travis and codecov in the list of checks.

This PR moves build smoke tests from TravisCI and migrates them to Github Actions. The result is that build tests are performed in parallel with unit tests and they don't hog additional resources on Travis. The workflow will not run if a PR only changes packages in the built-in repository, but will always run on pushes to develop or master.

* Removed build tests from Travis and passed them to Github Actions
* Store ~/.ccache in Github Actions cache
* Add filters on paths and make sure this workflow don't run
* Use paths-ignore and exclude only files in the built-in repo
* Added a badge to README.md

- also remove analytics beacon in README, which is not that useful
  anymore.

- all of Spack is Apache-2.0/MIT
- no packages are LGPL-2.1

This updates Spack's top-level metadata files to reflect the new
Apache-2.0 and MIT licenses.

- This isn't one of those autogenerated SVGs from a drawing program!

- This is a completely re-traced, minimalist SVG file with clearly
  delineated pieces so that your favorite renderer can draw a Spack logo
  at whatever resolution you want.

- Included versions with text, as well.

We moved to a new GitHub org! Now make the code and docs reflect that.

- Added a badge to show who's online.
- Added a section under "Get involved!"

- Update version guard in spack script to allow python 3
- Update min required version in the docs

* Switch from coveralls to codecov

- Add .codecov.yml, simplify .travis.yml
- Add codecov badge to README.md

* Add tests for spack graph.

* Major updates to Contribution Guide

* Grammar changes

* Fix missing/extra backticks

* Rewording, links, and tips added

- Docs are now visible immediately, and we don't have to push them
  separately.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>