don’t store minified css in development

- setup css defaults to non-minified css
- build minified css and jsversion on sdist/wheel
remove css sourcemaps from repo
attempt to regen source maps in git-hooks

if css changes
regen css (non-minified)

via `setup.py css`
add strict arg to css_js setup decorator

and attempt to build css on build_by (install)
`fab css` checks whether it needs to do anything

makefile-style

adds `force` arg to override, minify implies force.
check_call with list, instead of shell=True
post-merge is just a symlink to post-checkout
Merge pull request #6196 from minrk/git-friendlyish-less-css

Make less/sourcemaps a bit friendlier to git