rename WeakformProject to SimpleWeakformProject, and extract a new WeakformProject as an interface
rename WeakformTask to WeakformQuadratureTask and rename TaskUnit to WeakformQuadraturePoint
Simplify the function of WeakformProcess2D's constructor, add setter and getter for the key fields.

  - add a new field influenceRadiuCalculator
make WeakformProcessor2D only have a default constructor
make WeakformProcessor2D.prepareAssemblier() get rid of any argument
rename fields and function names from *weakformTask* to *weakformQuadratureTask*