Add RULE parameter support in GetLegendGraphic
Fix symbole size
Fix method signature for non rule based symbol
Get the right rule in Categorized and Graduated
Don't needed anymore

Without this the marker symbol is centered on the symbol place.
Fix GetLegendGraphic with scale on Categorized or Graduated symbol
Fix GetLegendGraphic with scale on non scale limited rule
Add missing test.

Witout this the scaleFactor in MM becomes 0.
Than we enter in a loop. For example on a GetLegendGraphic with a
line style as Steps
Merge pull request #901 from sbrunner/legend-rule

[qgis server] Add RULE parameter support in GetLegendGraphic