Liu 93 - Moving data drops to separate module

[pritchardn]

This PR moves most of the data drops out of drop.py and into their own dlg.data module, each having its own file. Some points worth noting:

• While the drops are split into their own files, the init.py added explicitly includes the support dataDROPs in that module. This makes it easier to import all supported data drops (from dlg.data import *) which at graph_loading makes the usage similar to having them all in one file like before.
  • While I think this is a good compromise, I'll gladly remove this if deemed unsightly.
• The json_data drop has also been moved into this directory
• The S3 drop has not been moved since the boot dependency is not explicit, nor is it tested (yet)
• BranchApp has been moved out into dlg.apps
  • As such, the tests will fail until a new dlg_example_cmpts release is available
• I have avoided moving io.py for now, I'd like to think about how to split that one up, if we'd even like to.
• The API documentation has been updated to include the various data modules

[pritchardn]

The PickOne component which was the dependency on dlg_example_cmpts has been removed.

[coveralls]

Coverage increased (+0.08%) to 82.277% when pulling e5575b4159394999c7275143b63d9b6cc026cc96 on LIU-93 into 1127ae4f47534da6ac350e4049b50294ef0c8c5a on master.