bug: fix view centering
Created by: acrisci
Make view initialization never fail instead of doing the initialization at some point in the future and flashing partially rendered content:
- fix xdg-shell so it emits the new event with window geometry (the first commit after ack_configure)
- pick the center output if no output is found under the cursor as a sensible default
Also, use the effective resolution of the output to determine centering so it works correctly on rotated outputs (this is understandably confusing and probably needs to be made clearer).