SpringAtom - fixes #119

ColumnConversionHelper v 0.0.1 ready
- resolves convertible pairs for given column
- has cache backend where key is calculated on columnClass
- pairs are resolved with sourceType being columnClass of RBuilderColumn

rbuilder.properties:
- added properties entry for 4 types of properties where each entry defines several possible conversion targets

ColumnTypeConversionBranch:
- defines branches of conversion meaning start point from which to start looking for convertible targets

PickColumsFormAction:
- updated to use ConversionHelper for RBuilder