Optimizations to the code that monitors and reloads images if they chang...

This is what I've done so far. I'm contacting you through github as you have been away in the IRC.

It doesn't work because line 353 of tileset.cpp     for(int i = 0; i<mTiles.count(); ++i)

gives me segmentation errors at mTiles.count()

It'd be nice if you could help me resolve this.
Please look at `qDeleteAll()` for this :) That function iterates over an container and deletes all items.