Fixes #1253, added annotations plugin that allows attaching notes to different days.

Notes:

  * Modified renderers so they would render arrays better. Before, arrays were added to DataTables and array keys were either lost or ignored, now they are rendered.
  * Fixed issue w/ JSON rendering that rendered arrays when the PHP arrays didn't have contiguous keys.
  * Augmented some exception messages.
  * Added utility method processRequest to Piwik_API_Request to ease use of the class.


git-svn-id: http://dev.piwik.org/svn/trunk@7612 59fd770c-687e-43c8-a1e3-f5a4ff64c105