[GSoC] Weekly Report #11 - Toolbars infrastructure via .ui files

[Szymon Kłos]

Hello,

Changes done last week:
- fixed crash occurring on some platforms while opening the file menu
- correct position of the popup menu on all platforms
- added placeholder icons for commands without an icon, icons are
aligned in the correct way
- hidden Notebookbar in the Start Center
- a lot of .ui improvements thanks to jphilipz who created doc with
ideas

Currently I'm working on 
https://bugs.documentfoundation.org/show_bug.cgi?id=101249 (toolbar
mode switching).

Regards,
Szymon