Refs #1984 - New plugins CustomVariables

 * Now possible to track up to 5 Custom variables per Visit. Also, Goal conversions will be reported 'By custom variable name & value' 
 * New report in Visitors > Custom Variables, new CustomVars API
 * Updated schema
 * Updated PiwikTracker PHP api to allow setting the name,value pairs

Code style
 * Refatoring some API code, and Archiving queries 
 * Changing text from 'segment' to 'dimension' as this is better description + we want to build actual segmentation later
 * removing getJs calls in some plugins since they only included sparkline.js, moved to CoreHome

git-svn-id: http://dev.piwik.org/svn/trunk@3780 59fd770c-687e-43c8-a1e3-f5a4ff64c105