Fix all top bars

[yexingsha]

Mocks in Figma.

• Background color: Headers above libraries/collections and items list and item detail should be slightly darker #55
• Horizontal padding: Use consistent 16dp margins across all screens and layout parts #66
  • e.g. in allitems screen, the "Select" button doesn't have enough right padding, and the search bar also only has 12dp padding.
• Font size: 17sp for both title and buttons; title is semibold (weight=600)
• The main part of the top bar (excluding system status bar and search bar) should be 56dp in height: 8dp top padding + 40dp button (either text or icon) + 8dp bottom padding
• The search bar adds another 56dp: 40dp search bar height + 16dp bottom padding
• The top bar should have 1dp bottom border (or is it drop shadow without blur? Not sure how this is implemented in code)
  • e.g. in login screen and itemdetails screen, the drop shadow has blur
• These sizing should ensure that on larger screens, top bars of different sections line up with each other On larger screens the header above the items list should match what we do on iOS #51

[yexingsha]

With the updated top bar background color, the current search bar color offers too little contrast. iOS uses #7676801F for search bar background, and #3C3C4399 for search bar label.