Manual in-game resizing

[Nightenom]

Addendum to #90
Should be on xml resLoc + modid basis
Allow for all UIs:

• override gui-scale additively, eg. vanilla settings is 2x, but user would like to have 4x

Allow for single primary resizable element:

• override gui size additively, eg. xml size is 320x240, but user would like to have 320x480
• override gui size anchor, ie. xml size (now) or screen size (fullscreen window type without scaling) - effectively enabling UI to follow screen resolution
• should be automatic or UIs having only one resizable element at root view (list or zoomdrag only?)