'tweak' plugin cleanup/reorganization

* Removed confirm-embark, stable-temp, patrol-duty
* Split (enabled) tweaks into separate files
* New tweak: manager-quantity
New tweak: import-priority-category
New tweak: farm-plot-select
Update documentation
New tweak: civ-view-agreement
Update dfhack.init-example
New tweak: nestbox-color
Merge remote-tracking branch 'origin/develop' into tweak-reorganization

Conflicts:
	NEWS
	Readme.html
	plugins/tweak/tweak.cpp
farm-plot-select: Actually check for crop validity
Merge pull request #349 from lethosor/tweak-reorganization

'tweak' plugin cleanup/reorganization, new tweaks