Include ddocs in sdist (#5896).

Soledad common package has a problem where it could not find the `ddocs/` directory when building the package for installation from source.

A proposed solution modified `setup.py` to only compiled the docs when the `ddocs/` dir is available and the `ddocs.py` file is not (https://github.com/leapcode/soledad/pull/167). That solution works to avoid the error when installing the package from source but doesn't address the question of exactly when the `ddocs.py` document should be compiled and exactly when the `ddocs/` dir should cease to exist.

It seems that the a better approach is to

1. include the `ddocs/` directory in the source distribution (because when people download the source distribution they want to actually read the contents of the `.js` files that generate `ddocs.py`, and
2. do not compile `ddocs.py` when building the source dist, but rather only compile it when building the egg and when installing in develop env.