----------------
- Renamed "project" to "layer tree" because it is clearer.
- Added "item definitions" to properly document and specify items such as menu
headers and projects. Their end result is a dictionary that will be returned
as json by the API.
- Added lots of documentation, including documentation generated from the
docstrings. The docstring documentation is carefully managed so that the
documentation as a whole remains clear and logical to read.
- Renamed "application" to "data source" as "application" looks too much like
"Django application". Inside Lizard, the icons in lizard-ui's interface are
also called "application icons", so we don't use this overloaded term here.
- Using version from ``setup.py`` in the sphinx documentation.