Plotgroups: copied Civ4BTS plotgroups

It's not called yet and does nothing. Savegames are currently unmodified.
Plotgroups: inline and just-in-time array
Plotgroups: city cache
Plotgroups: removed CvPlot::updatePlotGroupBonus()
Plotgroups: enabled enemy detection
Plotgroups: plots can add/remove bonus resources in the plotgroup they are in
Plotgroups: removed bonus yield code (precompiler flags)
Plotgroups: added python plotgroup class
Plotgroups: plotgroup spreads across plots. (not correctly yet)
[SAVE] Plotgroups: road connections work

Disabled code for all connections except roads.
Road connectoins are now fully functioning (limited testing)
Fixed saving/loading plotgroups.
[SAVE] Plotgroups: fixed loading old savegames+post load function

The tradeoff is that the savegames made with last commit can no longer be loaded.

Added postLoadGameFixes() to set up gamedata after a savegame is loaded.