use byte 61 in MCD

it's the "xcom facility item" flag
add a 3-dimensional array for base modules

a 6x6 grid, 2 deep, containing info on how many destructible objects
were present at map beginning, and how many were/are left now.
won't break saved games.

AI will be attracted to non-defunct modules, and try to destroy them.
anyone destroying a critical component will lower the "current score" for
that module, when this hits 0, AI will pass it over.
destroy facilities after base missions

so if the aliens (or you) destroy a facility during a base defense mission,
that may have certain consequences, like cancelling a manufacturing project
or destroying a craft.
destroy disconnected facilities as well.

if a base module is destroyed in combat, it may break the connectivity
of other modules on the base. account for that shit.
remove unused "destructible" flag from ruleset
Merge remote-tracking branch 'upstream/master' into WIP