emms: Add 'utl-emms-source-add-and-play'

Remove 'utl-emms-add-url' and 'utl-emms-add-and-play-url' - use
'utl-emms-source-add-and-play' as a replacement for 'emms-source-play'
instead.

Small changes in functions.
notifications: Use notifications.el instead of alert.el
process: Cleanup
color: Add message after loading a theme

Slight cleanup.
mode-line: Slight cleanup.
browse-url: Improve 'utl-choose-browser'