Separation of tests by folders and gate-docs fix

For unittests was created new directory and all such tests were moved
there. Also, .testr.conf was edited, where directory
magnetodb/tests/unittests' was set by default tox executing.

'tests.unittests.api.test_boto' and 'storage.model' were edited to back
compatibility with Python 2.6 and README.rst was updated with actual
values (stackforge) as well.

Also, 'sphinx' support was added.

Change-Id: I5d182644f692f4ca874185139cb72990040215eb
Closes-Bug: #1287144
Closes-Bug: #1287187