China fixes and improvements

Made AI able to take the Mandate in war, and buffed the temporary modifier given to a new Chinese imperial dynasty. Without this patch, the AI never seizes the Mandate; this often results in a permanently crippled Ming still being the alleged Emperor of China for many decades until it gets fullannexed and the EoC is dismantled, which eliminates a lot of flavor from Asia. 50 ws is a steep price to pay for a Mandate that comes with potential downsides, but for this issue the better solution is to make seizing it more desirable through temporary buffs for a new Mandate-holder, rather than to have the AI ignore and neglect it.
Rebalanced Celestial Reforms. Moved some effects around to better fit the flavor, and added some bonuses where the Vanilla modifiers were too underwhelming. A modest buff overall.
Buffed unique once-per-game leader modifiers for Nurhaci and Magellan.
Fixed Confucian harmonization checks in great projects and estate privileges.

See the extended description of individual commits for further details.

SpiritBaker / Difficulty-and-AI