Remove unused methods in CodeAssist
Refactor the various method generators

Since most method generators executed the same code just with different
values for the variables the DefaultValueMethodGenerator was added. It
contains the common code and all other generators simply pass the appropriate
variables via the constructor to the DefaultValueMethodGenerator.
Remove some obsolete classes

Instead of creating a class for each data type the EmptyMethodFactory
simply creates instances of DefaultValueMethodGenerator with the
appropriate values for the opcodes.