Add Buttons for functions

[muescha]

what:
add buttons (with icons) for function:

• to select a window to share
• for cropping the window

why:
it is also hard to get a right click working on my mac - for example CMD+click is not responding :( and tapping with 2 fingers also not working

[muescha]

since it is minimalistic UI - i found very late the menu with more options (additional windows) - the functions there should also somehow as buttons avaiable...