Add spells that target Targeting

[garykac]

Expand on the obfuscation spell (which prevents targets from being added to an area).

Add spell effects that trigger when your location is targeted by another player. E.g., force move the trigger to another location.

Be able to "follow" an opponent's target back to the original spellcaster.

[garykac]

Target an opponent's target to remove it.

[garykac]

Tracking in https://github.com/garykac/blockchain/blob/master/docs/spell-list.md