#934 PLCgen: Simplify bit size handling of numeric types, select smaller edge variable types.

Original changes:

• Targets have lists of types they support instead of just a size.
• Eliminate some type -> bitsize -> type conversion sequences.
• Delete the maxSupport(Integer/Real)TypeSize target methods.
• Add bit string types
• Use minimum size bit string types for for each edge variable.

Final end-user visible changes:

• No edge selection variables if automaton has not edges.
• Use bit type, rather than int type, for edge selection variables.
• Use smallest possible target-supported bit type for edge selection variables.
• Edge selection variables now have 0-based rather than 1-based values.

Addresses #934 (closed)