add gnome-music.in
use AC_CONFIG_FILES to update gnome-config.in

and rename gnome-music to gnomemusic
Add albumArtCache.py to the files to install

and fix a few imports
Make changes to gquintard work
Rebased on gnome-music master branch
Updated travis.yml
Fixes:

 * Restore widgets.py
 * Fix imports for local files
 * App can be stpped with Ctrl-C
 * Updated gitignore
Add signals import
Fix imports
Set data folder for resources
Fix 'gtk_application_prefer_dark_theme' property read
Set callbacks correctly
Use correct name for headerbar.ui
toolbar: correct stackSwitcher variable name
Correct variable name for self.toolbar.headerBar
Correct variable name for selectionToolbar
Update SONGS_COUNT name
Make useStack be optional, call __init__ with self