Reworked documentation sections

Split up the documentation based on who the information was targetted
against:

  - Info that's targetted towards power users was kept as top-level
    sections.  "power users" means people like admins/managers, people
    who want to run a local copy of amara, etc.
  - Info for programmers gets put under a new top-level section called
    developer's guide.

Removed some pages that were outdated and/or didn't contain much
relevent information.

Did some work to make the sections to use consistent header styles.  I
tried to follow the python guidelines
(http://sphinx-doc.org/rest.html#sections).  This fixes a bug where
the babelsubs sections were getting pulled into the top-level TOC.

Updated the testing documentation.