Abbreviate quantity overlay on icons

If a quantity is over 1000, we remove the last 3 digits (integer divide
by 1000) and add a "K" suffix. Then the actual total is displayed in the
item's long tooltip next to its name.
Merge pull request #704 from dorkster/bugfixes

Check inventory stacks for slots with a quantity of 0 during save/load
Move kilo abbreviation to Util function and make "k" translatable
Remove unnecessary variable
Merge pull request #705 from dorkster/quantity_abbr

Abbreviate quantity overlay on icons