Add menu bar to ui

[nyxxxie]

The menubar is that little bit on the top of a window that contains [ File | Edit | Windows | ... ]. We should add one that contains the following.

• File
  • New - creates new file in current project
  • Open - opens existing file and adds it to current project
  • vertical line
  • Save - Saves currently focused file
  • Save As... - Saves currently focused file as
  • Save All - Save all opened files
  • vertical line
  • Quit - Exits program
• Edit
  • Undo - Undoes last change
  • Redo - Redoes last change
  • vertical line
  • Cut - Redoes last change
  • Copy - Redoes last change
  • Paste - Redoes last change
• Windows
  • Somewhere in here should be a submenu that is populated dynamically somehow by all dockwindows currently added to mainwindow. Clicking on a window should hide it

Implementation for specific menu actions is optional, the implementer can just use actions with empty bodies if they wish