[qgis server] Add RULE parameter support in GetLegendGraphic

Especially with the new RULE parameter I see that the icon is one pixel smaller than it should be 
Fix symbole size 	bc5cf20

When I introduce the scaleDenominator and rule in the mane class method signature I miss to change all the children method signature
Fix method signature for non rule based symbol 	996a5f3

Implement the rule filter in Categorized and Graduated
Gett the right rule in Categorized and Graduated 	0b4db7f

Before this the marker symbol is not centred on the symbol place (on top left corner).
Don't needed anymore … 	4545858

Fix GetLegendGraphic with scale on Categorized or Graduated symbol 	cc193c8

Use the already exists method isScaleOK
Fix GetLegendGraphic with scale on non scale limited rule 	5ac0ecd

Without this, the scaleFactor in MM becomes 0 in https://github.com/qgis/QGIS/blob/master/src/core/symbology-ng/qgssymbollayerv2utils.cpp#L2555.
Than we enter in a loop. For example on a GetLegendGraphic with a line style as Steps
Add missing test. 2de9426153b0e0beacc07e6ff7b0cd9cdc83d4da