Closes #1337 - Adding support to generic attach for categorical and segarray

[joshmarshall1]

This ticket (closes #1337):
This ticket also closes #1284:

Added methods to RegistrationMsg.chpl for generic attach command which takes in an optional type or will attempt to infer the type if not passed. Passing in the optional type will skip directly to the portion of the method that compiles the response message. This should allow users to pass the type to increase performance.

I added a method to MultiTypeSymbolTable.chpl that checks existence of a given name and returns a bool result. I didn't see any other methods that returned bool for checking existence, only checkTable which returned void if the name exists, or error if it doesn't. This new method prevents me from having to use a try/catch block with checkTable or having to access the tab property of the SymTab class directly.

Also added were from_return_message methods to categorical.py and segarray.py so the return could be passed from the generic attach method in util.py and parsed correctly by the corresponding class.

The existing test cases for pdarray and Strings generic attach were expanded to include a given and an inferred type test. Two new tests were added, one for Categorical and one for SegArray, also each with a given and an inferred type.

[Ethan-DeBandi99]

Logic all looks good. One thing that I would like to change would be using + for all delimiters instead of ;. I see why you are using a separate delimiter here (Categorical.categories being a Strings object). That should be easy enough to glue together to create the Strings object properly using Strings.from_response_msg().

[Ethan-DeBandi99]

Looks good

[mhmerrill]

@joshmarshall1 there is a basic conflict on this PR now. I could fix it but I rather you did so I don't screw it up with the web editor ;-)

[stress-tess]

Couple gripes but overall the logic looks good!

[stress-tess]

Looks good!