Removed cooldowns
After considering, I've determined that the idea of a cooldown itself is
against the design of Spellmasons. This was just a bandaid to
a few select spells being overpowered. I've found it better to
alter the spell logic itself (in the case of freeze to not allow stacking)
and to make them more mana expensive (in the case of resurrect)
which will prevent them from just being cast turn after turn.

Also the modifier itself can prevent the unit from being
refrozen (see freeze) which is much better than cooldowns
because it also prevents refreezing in multiplayer.

Balance: Freeze
Removes cooldown
Freeze no longer stacks

Balance: Increase Merge spell rarity

fix: Prevent empower from targeting players to prevent confusion
i18n: Clarify that Empower does not affect players

art: Add slightly new cast animation

audio: Only play "endTurn" sfx once per turn
Thanks Hazzie and Nord from Youtube for
this suggestion!

fix: Backfill stat upgrades for players who
join late.
Thanks Waterbending Squirrel!
Fixes: #567

audio: Smoothly switch songs
Don't switch songs every time a level is beaten, switch
when the song is done
Closes #805

content: Add Ultra Clone as upgrade to clone
in order to balance out the clone + merge exploit which
was mainly possible because clone with adding the clone as a target
yields exponential results when stacked. Now the basic clone does
not add clones as a target

fix: Intercept END_TURN message
and do not send the original. Send a new END_TURN message as client with playersTurnEnded attached.
(Note: this already worked except it still sent through the original END_TURN message, this fixes the original from being
sent through and only sends the transformed one through)
Resolved: #811

log: Improve error message for proper aggregation
on remote logger

experiment: MultiColorReplaceFilter
Decrease epsilon for blood golem to see if
it resolves #695

UI: Fix default "Refund" text
Before if no text was provided, none would appear for refund.

balance: Exclude Execute from starting damage spells (#807)
- Since it cannot deal damage on its own