0.2.1 Misc UI Tweaks

This MR provides some UI tweaks that I ran into after dogfooding Briar Desktop for the past couple of weeks.

• Reverted button padding on "Add Contact", "Add Picture", and "Cancel Introduction" buttons
• Reduced padding around online indicator to allow for better use of space on Contact Cards
• Fixed bg color on introduction drawer to surfaceVariant everywhere (previously the bg color was not uniform throughout).
• Made introduction drawer header "X" button actually line up with contact list (was off by a few pixels before)
• Introduction drawer now centers profile pictures and alias'.
• ProfilePictures and MessageCounters now use 1px borders to better match briar android.
• AddContactDialog now uses correct typography in TextInput placeholders.
• Remove ConversationList padding, the scrollbar for private messages now lives in the "gutter" between outgoing messages and the window's end.
• Bump font size of ExposedDropDownMenu to typography.body1 to match everything else.
• Add auto-formatting rule that fixed ktlint problems I was running into.

Before:

After: