fix & refine build placing, refine nuke & antinuke behaviour

fix bertha, nuke, and nano build placing

only stockpile nukes & antinukes if done and are needed

only place two of any one type of defense at a turtle point, one if low priority

only build fusion if enough metal and energy
overhaul siege check, fix turtle priority total, other

siege check based on mobile/immobile threat ratio

siege units in limited numbers based on attackcounter

nuke silos in limited numbers based on combat count

improve nuke targetting

slightly change targetting values, add techlevel modifier

improve attacker stuckness heuristic
unit counting overhaul, scout order bandwidth fix

- fix scout behaviour sending too many orders (related to idle)
- don't build second fusion immediately after first
- don't built second adv factory immediately after first
- keep track of number of each unit type in ai.nameCount rather than
looping through friendlies
- nukes won't build or stockpile if antinukes are seen in the last
thirty seconds
- check for dangers moved to targethandler, resulting in more consistent
behaviour
fix scout stall after attacking
count mexes for fallback siege check

removed airplane metal spot duplicates
build slightly more siege units
Merge pull request #24 from zoggop/master

overhaul siege check, danger checks, own unit counting