Flatten-out the View menu

Rationale:
----------
* Existing View menu already contained Editor-related options
  like "Change Font" and Zoom controls, so it makes sense to
  group all of the View-related items together.
* Anecdotally, some users have been unable to easily discover
  the Color Schemes changer dialog because it was nested under
  a submenu.
* Distinction between "Editor" (Scintilla) and "Editor" (All
  of Geany) is likely non-obvious to most users, especially
  new users exploring the menus.
* There's not very many items to cause scrolling on low-res
  monitors, and the View menu still has less items than the
  Document menu.