Use outlined button style
This branch adds an outlined button style that can be used for secondary actions that currently use the borderless button style. Dialogs (including full-screen dialogs) continue to use the borderless style.
This branch also updates the OfflineFragment in the mailbox status UI to use the same pattern that's used elsewhere for dealing with small screens.
Closes #2400 (closed).
Hotspot setup UI showing a negative button:
Mailbox status UI showing neutral and negative buttons:
Offline fragment showing layout adapted to small screen (the large icon is hidden and the buttons are outside the scrollable area to ensure they're visible):
Draft because it depends on !1745 (merged).