* fix issue #4341
add testEnum
if you set enum as json value then it will be cast to int

* add behavour for enum into VarHolderImpl
add tests for enum classes with differnent underline integral types

* replace static_cast with convertTo* methods, they can chaeck types and
limits

* fix missing types for convert methods

* fix code style
add testEnumType to the VarTest.cpp, extract() works