CMParts: Allow CompCache size to be set by user - via % of total RAM

Use % instead of a set size - per suggestion from Cyanogen
Fix to integer instead of decimal being passed around - props to Nameless
Handle older versions changing enabled CC to Default CC size (25%)
Enable PerformanceSettings dialog to view new CC setup
Final cleanup and fix default values / bash arithmetic

Change-Id: Ie7525cfa1f8829bb037961a66620ab8664f39cec

German translation - Matthias Büchner
French translation - Sébastien Vaucher