Remove old type chaging code

This also deletes the service that was going to keep the menu entries up to
date.
Simplify isBounded() definition

Previously one could define a type that is bounded above but not below (and
vice versa). This seemed a tad bit complicated. I'm going with YAGNI here.
Improve DataType naming and use when possible
Rename BetterTypeChanger to TypeChanger
Maintain metadata better
Comment out unsupported types

I have defined four data types that aren't quite supported yet: 64-bit and
128-bit complex types and unbounded integer and float types. I have now
commented out their @Plugin annotation. This keeps them from being
discovered by IJ2.

When we iron out the type system so that Datasets can be made of these types
we simply need to reenable the @Plugin annotation to make them available.