make GetSpawnOccupants more robust against invalid list queries

fixes #5588
Add tech levels to TD.
Remove super-spammy debug messages.
Reorganise AI base building logic.

- Now obeys defined structure percentages and limits.
- Faster.
- More readable and maintainable code.
Fix the bogus D2K AI definitions.
Fix NRE if a unit is damaged without a warhead.
Merge pull request #5894 from pchote/warhead-nre

Fix NRE if a unit is damaged without a warhead.
Merge pull request #5833 from pchote/cnc-techlevels

Closes #3221
add parachute corpses

fixes #5893
check if the host building is gone

fixes #5670
bring it in line with Rearm
Merge pull request #5890 from Mailaender/negative-spawns-crash-fix

Made GetSpawnOccupants more robust against invalid list queries
Merge pull request #5892 from Mailaender/destroyed-repair-building-nre

Added a check if the rearm host building is gone
Merge pull request #5896 from Mailaender/d2k-parachute-corpse

Fixed missing parachute corpses in Dune 2000
Restore blinking ready label in RA.
Merge pull request #5897 from pchote/disable-green

Restore blinking ready label in RA.
Change defaults for the production palette's ready sign

Default is now to blink alternating between white and gold.
Merge pull request #5899 from obrakmann/blinky-blinky

Change the colour of the blinking READY to gold
Update .travis.yml

remove failing auto-wiki-update
Add tech levels to ra