ai_helper.get_closest_location(): fix bug with tags in SLF

The way how the Standard Location Filter was dealt with only worked
with keys, not tags.
Messenger MAI: fix bug with escort units blocking the messenger

When there were lots of escort units, they previously quite frequently
blocked the messenger’s way, preventing him from making progress even
when it was possible.  Escort units now specifically move out of the
way if they do not need to attack enemy units in the messenger’s way.
MAIs: minor code simplification in AIs that take both [filter] and id=

These are the AIs that used to use Behavior Candidate Actions (BCA).
Patrol MAI: fix bug with save/load persistent data storage

WML values may not be used as keys, this can make savegames invalid.
Store information in the units now rather than in self.data. (Note:
storing in self.data would also be possible if the syntax were changed.)
fixup b854aab437f157eea642131b882a4987a95c5b6b (ai side drops)

logic error was introduced in client side controller types:
when a player drops and controls an ai-side, the side_drop signal
is only sent to the host, who should make that side a local ai,
not a networked ai.
don't show petrified units in "Damage versus:" tooltip

since we can't attack these, this information is not useful.
afaik it is quite common to have permanent "statues" in MP maps,
and extremely rare that units may be unpetrified in any core or
umc scenarios.