This adds a style.css file to allow the use of custom css
Fixes https://source.puri.sm/Librem5/calls/issues/115:
- Making the phone number larger
- Moving the delete button to the bottom
- Rounding all buttons, and making the grid buttons circular
- Making the call button a bit less wide
* Make the Answer button look nice and laid out properly.
* Merge the time and status labels, displaying simply the text
"Calling..." until the call becomes active and then the call time
afterwards.
* Fix info display bar in both the call and main windows so they use a
GtkRevealer and work a lot better.
* Add a "new-call-symbolic" icon for the "Add call" button.
* General tweaks and clean-ups
Closes#55Closes#35
