Made the grid size customizable

Many users have asked for an option for customize the grid size. So, now users can define the grid size in the Preferences dialog (General->Grid).
The camera distance is set to 50% of the grid size with a minimum value of 8 wings3d units.

NOTE: Added option to customize the grid size.
Added new option to Absolute->Move command

That option was added after an user ask for a way to chose another vertex reference than the centre (the default value).

NOTE: Added a new option to Absolute-Move command (MMB) that enable the user set the reference point.
Merge remote-tracking branch 'micheus/mv/absolute_move_reference'
Fix paths with spaces

17.0 uses long windows filenames which by default installs erlang
in a path with spaces.
Merge remote-tracking branch 'micheus/mv/grid_size'