This commit refactors how global configs are merged on theme upgrades.
Now, global configs will always have the same "structure" as the incoming
config, instead of sometimes placing properties in seemingly random spots,
if the two configs don't match up exactly in terms of structure.

Per Rose's request, the sdkVersion is now always updated to the incoming
config's value. Besides that, preexisting properties will favor the
original config, while commented out properties will favor the incoming config.

Properties and comments in the original that do no exist in the incoming config
will be moved to the bottom of the config.

J=SLAP-1717
TEST=manual,auto

ran an upgrade