refs #3013

 * plot multiple metrics using $columns (renamed from $column)
 * plot row evolutions using optional $labels, will plot top 5 labels when omitted
 * imageGraphEvolutionUrl added to report metadata (only for reports without constant row count and Referers.getRefererType)
 * $showMetricTitle renamed to $showLegend

refs #3014
 * new report parameter 'Show Historical Graphs for the top 5 values'
 * better looking evolution graph on landcape pages

refs #3158
 * $label is now optional, will return top N=filter_limit row evolutions sorted with filter_sort_column when omitted
 * support for $idGoal
 * integration tests updated

constantRowsCount set on
 * Goals_getDaysToConversion
 * Goals_getVisitsUntilConversion
 * Referers_getRefererType

merges
 * r6874

IDEA
 * in Piwik UI, add a link 'display top 10 row evolutions' using API.getRowEvolution &label=false&filter_sort_column=xyz&filter_limit=10
 
TODO
 * fix scheduled report integration tests
 * review @reviews

git-svn-id: http://dev.piwik.org/svn/trunk@6918 59fd770c-687e-43c8-a1e3-f5a4ff64c105