b19_3: Balance Update + Smaller Fixes

[list] [*] "Enemies start with -x% HP" no longer stacks. Only the highest effect is applied, up to a maximum of -25%. It won't trigger again after fleeing. [*] Charm chance is now capped at a maximum of 75%. [*] Increased charm penalty buildup after level 3. [*] Increased chance for bosses to block doors. [*] Slightly nerfed healing (reduced gain from merging, slightly lower base values, and a smaller increase from stats). [*] Slightly increased enemy power level scaling. [*] Limited dropped items to a maximum of 3 effects, down from 5. [*] Lowered percentage value caps on ability-related item effects (reduced to 25% max, down from 85%). [*] Fixed an issue with the Merge-O-Mat and Meat Grinder consuming side slots, now capped at a 40% chance. [*] Fixed a crash related to the Tinkerer. [*] Fixed upgrade point notification appearing unnecessarily. [*] Added a "Disable audio when window is in background" setting, for everyone playing at work. [/list]