Prevent multiple bridges spawning at the same location.
Fix bogus pathability check.

This fixes units on pathable bridge tiles from
being killed on bridge death (they were failing
the check against themselves).
Rewrite Enter and related activities.

The unit will now path to the nearest adjacent cell, drag inside, do the inner activity, then (if still alive) drag back to its original
location.

This fixes:
 - Mismatch in logic between Enter and MoveAdjacentTo,
   which causes an infinite loop.
 - Building capturing failing from certain directions.
 - Being unable to enter buildings on unpathable tiles.
 - Units being stranded inside a building if the requirements
   for the inner order aren't met.
Add Selectable field to Selectable.

There are a bunch of bogus assumptions about
targetable actors being selectable. These aren't
easily fixed, so this add a Selectable field that
can be diabled for things we want to target, but
not select.
added separate explosions.yaml for weapons
explosions added in weapons/ folder; defaults l8r
cleaning up pre-requisites: refinery
rename e3 weapon 'bazooka'; removing aa for now
necessary fix for mod.yaml... was broken
Gave buildings except turrets AutoTargetIgnore
Doesn't really make much sense to auto-target buildings that are no
threat. Units should fire at units or turrets.
Fixed attack dog voice
Update ViewportScrollControllerWidget.cs

Moved Scroll() out of the if statement checking to see if edge scrolling was enabled thereby fixing bug introduced that stops keyboard from working if edge scrolling is not enabled.
re-ordered structures list
changed cost of various structures.
money is limited, shouldnt be wasted on pointless things that take extra
time building for no reason. Like, power stations, barracks.
Some changes inspired by original dune 2000 stats. Other buildings left as
is, because we're not trying to copy the original game.
Light factory made super cheap to distinguish it from heavy factory. It
should make poor-man's units, relatively quickly. Things that sort of
suffice at countering better heavy units like tanks, while pursuing a
different strategy.
No buildings cost more than $2000, because it's not really necessary to
have things be that expensive (from what I can tell). It just wastes time
and cuts down possibilities for strategy by making certain things out of
reach and forcing everyone into similar strategies.
Research facilities that unlock units (outpost, high tech factory,
research facility) all ~1000.
Starport made 2000 so that it's not too cheap since it's good, but not
inaccessible as a mid-game strategy.
fix artillery explode

For some reason artillery wasn't exploding. I had set it at 75% odds last time I edited it. Just making it explode again.
It really needs to explode. It only costs $600 and is pretty powerful. This is its drawback, to make it vulnerable if player bunches them up.
Merge pull request #3067 from ScottNZ/dog

Fixed attack dog voice
Merge pull request #3069 from psydev/patch-1

fix artillery explode
Merge pull request #3068 from twhitney11/twhitneyKeyboardScrollFix

Fixes #3049 Deselecting Edge Scroll Loses Ability to Use Arrow Scroll Too
modified custom pre-requisites for buildings
changed unit costs at starport; fix starport