Redo Value Classification UIs

A lot of code was refactored and pushed up to PnlAbstractTableAnalysis
in order to ensure consistency between Value and Interval
Classifications. This also removes a lot of redundancy.
Refactor: Consolidate onVertex/onCentroid methods

Previously there were three different implementations of the
onVertex/onCentroid panel. I consolidate all three of them into one in
this helper class.

Note: "Place symbol on" will be translated by "Placer le symbole sur".
Then there should be plenty of room for the radio buttons.
Add forgotten file from last commit
Merge pull request #480 from agouge/ui/value-classifications

Facelift for Value Classifications