option: Interface option for centered menu scrolling.
uimenu: Scrollbar place indicator for large scrolling lists.
Scroll indicator: No hiding, actually apply color option
Remove the vhtype_id enum; vehicles are now referenced by name.
Documentation update.
Fix dispersion comparisons
Stop underwater weather effects
Add power armor acid rain protection effects
Merge remote branch 'origin/master' into scrolling_option_and_indicator
uimenu: scrollbar has better position calculation, consistent size >= 2.
Formatting tweak
cleanup
Increase ketchup spoilage time
Added Scrollbars to various lists.

Code based on atomicdryad's PR (https://github.com/CleverRaven/Cataclysm-DDA/pull/2843) with a few changes to the scrollbar calculation.
Added the Top/Bottom scrolling option to compatible lists.

There are still a lot of menues left that would have to rewritten to support that behaviour.
Added scrollbars to two more lists.
Bigger Scrollbar on smaller lists.
-changed "throw_from_seat": Passengers aren´t thrown from the seat when there´s a seatbelt.
-fixed a bug in a json file
Add separate ID field to vehicles.json to facilitate i18n.
Lower enc layering penalties
Reduced chewing gum frequency, except on military drops.