As discussed, fixes and improvements to our config file system

- All of our config files have been merged into one
- Local config options can now be merged per-key rather than
  overriding the whole section, so missing keys in the local
  config file will fall back to the value from the dist file.
Adding some global configs to maintain compatibility with old default settings.
Merge pull request #193 from girder/config-loading-bugfix

As discussed, fixes and improvements to our config file system