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

This commit removes the `python_version.py` unit test module
and the vendored dependencies `pyqver2.py` and `pyqver3.py`.
It substitutes them with an equivalent check done using
`vermin` that is run as a separate workflow via Github Actions.

This allows us to delete 2 vendored dependencies that are unmaintained
and substitutes them with a maintained tool.

Also, updates the list of vendored dependencies.

This reverts commit 54e3bc31.

Use `spack pkg changed` and `spack maintainers` to figure out which
packages changed and who their maintainers are in a PR.

Add any maintainers to the PR as reviewers.

- Trying to reduce the number of top-level files in Spack.

- CODE_OF_CONDUCT.md can be referenced from the README.

- CONTRIBUTING.md is only used to display a message on pull requests, and
  it still does that when in .github.

1137b183 removed the -s option from spack such that to see a stack
trace you must pass the --stacktrace option. The bug report templates
were not updated accordingly.

The original numbering was not incorrect markdown but this is easier to read.

This replaces the single github issue-reporting template with templates for the
following types of issues:

* Build issues
* Spack command errors
* Feature request

Each template includes suggestions which are generally useful for the type of
issue encountered.