Chem grenade fixes

Fixes #3986

- Foam reagent inheritance fixed:
The trans_to() proc in Chemistry-Holder.dm was calling handle_reactions() every time it would add and remove reagents with add_reagent() and remove_reagent(). I've added a safety flag to both of these procs (and copy_to()) so that trans_to will not call handle_reactions() until it has added all the reagents to the target container. This allows foam to reliably take on the properties of other leftover reagents.

- Fixed a bug in effect_system.dm that wasn't applying reagents from foam to the environment.

- Tweaked smoke to apply reagent effects after it has stopped moving
This was causing huge reagent spam at the center of the smoke cloud as it was spawning, since they were being applied every time the cloud of smoke moved. Also changed it to apply the effects 2-3 times at longer intervals (2 seconds).

- Smoke also only effects tiles in a 3x3 grid now, rather than 5x5.

- Summary:
Chem smoke does slightly less damage (if it contains damaging reagents)
Chem smoke proc calls reduced by 60-70% (significant lag reduction)
Foam works properly again
Foam proc calls reduced by 70-80%
Fixed cable colors

- Fixed a couple of lines of code in power.dmi so that cables correctly update their color
- Fixed the contrast of the cable icons
Merge pull request #4416 from Loganbacca/foam

Chem grenade fixes