NEXXT studo 3.1.0 released - minor new features and bugfixes

Some more fixes, along with a few new minor additions:

Shortcut changes:

• Replace tile: 
  Now: Alt + R (Was: Ctrl + R)

New features:

• Reload session [ Ctrl + R ]:
  Will ask permission before proceeding.
  Reloads session if a path exists.
  Otherwise reloads starting conditions.

• Copy tile properties (as C header):
  Found in Menu > Patterns
  Will put the current tilesets' collision properties on clipboard.

Improvements:

• -Import PNG:
  Now supports 1-bit (2-colour) PNG:s. 
  Works for both import as canvas (nametable/map) and as tileset.

Bugfixes:

• Save tile properties; 4 sets (.tprop):
  Despite saying 4 sets it really only saved 2; the old behaviour when the ui only had 2 hot-button sets.
  Fixed.

• Copypasting:
  If copying tiles by reference (copy nametable/map selection, paste on tileset), and the selection copied was larger than can fit the tileset buffer, repeated memory access violations would occur.
  Now fixed to accept reasonably large tile buffers (ignoring the excess when laying down new tiles). 
  In addition; if there's more than 1024 tiles (4x what can be pasted to the tileset anyway), nexxt will give a warning that something likely done by mistake has happened, and ignore the request. 

• Navigator:
  -The bounding box of the 2nd camera (magenta) only displayed bottom and right boundaries when in 50% zoom mode, because of a nearest-neightbor error.
  Now displays all 4 sides as intended. 

• MMC2/switch tile mode, while swapping tiles on tileset:
  Drag-dropping tiles to swap them would repair the nametable/map as if in normal mode; this would jumble on-screen content that are pointing to tilesets unaffected by the swap action.
  Now fixed.  

• Global PPU mask B:
  Loading certain old session files, this wouldn't be initialized properly.
  Fixed.

• Scale 1x (secret scale mode; [ctrl+1])
  In this reduced-ui mini mode, grid button "x8" would be misplaced.
  Fixed.
  

Other changes:

• -Swapped places of some menu items in the "view" menu, with the intention of easier navigation.