Fixes #2434 Now Actions.get* and Goals.get* (which were the two API not supporting all segments) have full support of all segments + adding tests

Refs #2432 
 * Processing Custom vars per page: they are merged in the existing Custom Variables output (rather than create a separate one)
 * So there is no need for a new Report in the UI, Custom variables of scope "page" are displayed in the "Visitors > Custom Variables" report
 * Displaying Custom vars per page in the Live API output


git-svn-id: http://dev.piwik.org/svn/trunk@4717 59fd770c-687e-43c8-a1e3-f5a4ff64c105