Migrate ParseGlobalConfig to new database storage API.

[nlutsenko]

Also fix the thing, so it properly upserts if config does not exist.
This is modeled close to how parse.com works.

[drew-gross]

Sweet! Have you tried this with the dashboard?

[codecov-io]

Current coverage is 91.73%

Merging #901 into master will increase coverage by +0.05% as of b1cb0e8

@@            master    #901   diff @@
======================================
  Files           71      71       
  Stmts         4102    4103     +1
  Branches       850     851     +1
  Methods          0       0       
======================================
+ Hit           3761    3764     +3
  Partial         10      10       
+ Missed         331     329     -2

Review entire Coverage Diff as of b1cb0e8

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[nlutsenko]

Nope, not yet, can do, but probably a bit later...