Allow individual evolutions to be applied

Fixes #2436

Also did a refactor of the way evolutions configuration is loaded,
deprecating the old configuration names, and namespacing everything
play.modules.evolutions.*.  Every configuration item can now be
configured globally as well as at a per datasource level.
Merge pull request #2436 from jroper/2436-disable-evolutions

Evolutions plugin tries to lock datasource before checking if evolutions are even supposed to be run against the datasource