advanced digitizing tools
this integrates advanced digitizing tools aka CAD tools in QGIS application and basically a port of CADinput plugin
* new class QgsMapToolAdvancedDigitizing shall be subsclassed if adv. digit. tools could be used in a map tool
* QgsAdvancedDigitizingDockWidget handles the interaction with the user and also perform the constraints (filters events)
* QgsAdvancedDigitizingCanvasItem paints construction lines on the canvas
Merge pull request #1624 from 3nids/cadtool_single

Advanced digitizing tools (aka CAD tools)