Reimplement temporary mana using GameTag.TEMP_RESOURCES

This is, unfortunately, how it's implemented on the server. I really preferred
reusing oneTurnEffect and buff slots, but hey ...
Deprecate usage of data.<tag> wherever possible in favour of proper GameTags

This gets rid of the attributes we don't actually use much from XMLCard.
Why? Because instead, we want to use Card.tags, seeing as the data cannot be
silenced or modified etc.
Implement Entity.getIntProperty() and getBoolProperty()

This stuff will replace getProperty() soon enough.
Look in card definitions for GameTags as well

This allows us to define GameTags from card definitions without having to
define a verbose GameTag.HEALTH: 5 ... dict or some such.
However, this does force us to change the API, as we can't have conflicts:
 - atk becomes Atk
 - health becomes Health
 - charge becomes Charge

Not all of the properties have been ported yet - a job for another day.
Reimplement charge using getBoolProperty(GameTag.CHARGE)
Reimplement health and atk using getIntProperty(...)
Reimplement auras

Nth time's the charm.
The Game object still holds a list of auras, but auras are now better-behaved.
They will actually buff minions affected by them, and clear buffs when they get
destroyed. This is possible thanks to a new "onUpdate" event.
They will also keep a cache of minions they already buffed so that they do not
constantly remove and reapply themselves (that would break a lot of rules).
Implement Lightspawn, with tests
Add more positioning and weapons tests