AI disposal interaction.

The AI can now interact with disposal units and turn the pump on/off.
Fixes light going through walls.

See https://github.com/tgstation/-tg-station/pull/5972 and https://github.com/tgstation/-tg-station/issues/2788.
Fix most nullspace items, rewrite floor tiles not to del() on every place/remove
Typo fix
Bugfix.
Add defines, change comment
Fixes and guards against strange values
Adds my approved custom ai core sprite.  I think I did it right.
Merge pull request #7131 from GinjaNinja32/nullspace

Fixes most nullspace items, rewrites floor tiles not to del() so much
Merge pull request #7134 from Segrain/dev

Bugfix.
The stars() helper proc no longer breaks HTML tags
Papers will now have a nice description like every other item
Ghosts can view paper from anywhere, improved the 'far' message
Renaming paper to its original value will now revert it to initial, not just 'paper'
Whitespace changed by saving in DreamMaker
Merge pull request #7110 from PsiOmegaDelta/Disposals

AI disposal interaction.
Merge pull request #7112 from PsiOmegaDelta/LightningRealLightning

Fixes light going through walls.
Merge pull request #7143 from Amunak/paper-fix

The stars() proc doesn't break formatting, improved papers
Merge pull request #7138 from Neerti/11_25_14_neerti_ai_core_custom_sprite

Adds my approved custom AI core sprite.