0.18.3 - "Fill with numbers" improvement and 3 bugfixes

Some more bugs ironed out; 2 relatively new ones, and 1 really old. 

Opening files by association works again, 
Capital S and O no longer causes problems when typing,
and a small memory leak has been fixed.

That's it for those. 

Now on to the newest feature. 
The "fill tiles with numbers" (Patterns > Generate > ... ) now works on selections of tiles; both box- and multi selections. 
Especially combined with "Find unused" and "Find duplicates", this provides an easy way to single those out more permanently, while providing useful information about them.