osx: Further optimizations, show GTK spinner when working

OSX - new wrapper script, no_chdir, -O2 compile option for environment

Mojave support & jhbuild environment update

1. Force always release mode on OSX

2. Ensure py2app finds pyobjc
3. Smaller package size

Upstream sync

Handle all args

Update version string in our build, too

Allow the user to set the GTK theme from enironment variable

Merge branch 'master' of https://github.com/yousseb/meld

It finally workd