property editor attribute rendering enhancement

- check attribute meta definition to see if the attribute is common
among the selected nodes
- if attribute meta has enum options dispaly values as dropdown
remove console.log
add method getValidConnectionTypesInParent

to return all the potential connection types for apsecific source in a
specific parent that can be instantiated
update sidepanel padding values
remove unnecessary stylesheet
style updates
METAAspectHelper have been added to constraint manager so it is now can be used in constraints...
Merge branch 'demo' into develop-r