MAINT: Use setuptools_scm for versioning

[larsoner]

In many repos I work with we've moved to setuptools_scm for version control. It's great because when you cut a release on GitHub with a tag like 0.10.0, that will automatically show up as the version in PyPI and sdist, but the next PR that gets merged will show up as 0.11.0.dev<bunch of info>. It thus adds info and gets rid of the need to manually tick versions -- you can just cut a release on GitHub and be done.

The only downside I've noticed is that downstream packages need to do git+https://github.com/pyvista/pyvistaqt to install latest main rather than using a zipball, but this is a minor drawback and easily worked around I think.

[codecov]

Codecov Report

Merging #356 (0ff990b) into main (6d22f16) will increase coverage by 0.59%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #356      +/-   ##
==========================================
+ Coverage   96.72%   97.31%   +0.59%     
==========================================
  Files           8        7       -1     
  Lines         671      671              
  Branches       82       82              
==========================================
+ Hits          649      653       +4     
+ Misses          3        0       -3     
+ Partials       19       18       -1     

[larsoner]

I'll merge this and give it a try in 0.10.0. If it ends up being problematic we'll revert!