TypeParams added to AddMethod

Type parameters are added for def construction in AddMethod refactoring.
Current implementation limitation:
there is an issue if pass several type params to mkDefDef inside addMethod (inside AddMethod class).
To overcome this issue in the commit all required type parameters names are grouped in one passed typeDef:
val typeDef = new TypeDef(NoMods, newTypeName(typeParameters.mkString(", ")), Nil, EmptyTree)
this typeDef is used while constructing result newDef in mkDefDef.
AddField refactoring added

Similar to AddMethod, intended for val/var creation.
Current implementation limitation: var printing is implemented with direct
var addition (otherwise var is not printed):
NoSymbol.newVariable(newTermName(s"${nme.VARkw} " + valName))
AddField/AddMethod refactoring
Merge pull request #49 from VladimirNik/abstract-members-implementation-api

Added: AddField refactoring, type params to AddMethod