Better touchscreen and adaptive UI support

Touchscreen:

• overlay zoom buttons for easy access
• context menus can be accessed #171 (closed), #182
• text can be selected
• selections can be changed afterwards #181
• annotations can be moved

Adaptive:

• main view fits 360px
• header bar is split
• sidebar visible state is restored when window size is increased again
• overlaid sidebar collapses when something in the view is to be shown (e.g. search result clicked) #153 (closed)
• annotations can be viewed, and changed #183
• PpsView uses double for coordinates for better scale factor support #175
• multiple tabs shown in one window #54