Revert "remove Dimensions and Reports to avoid huge upgrade query on DB:"

This reverts commit 49ae6b4030e83a9e0b5a842810c7ddda3c322b24.
created an exampleTracker plugin which is disabled by default so those columns will not be installed
refs #5926 move reports to exampleReport
Merge branch 'master' of github.com:piwik/piwik