Implement 2017 DS client connection support

[auscompgeek]

Note: I have not had a chance to test this. If a kind soul would be generous enough to test this with their driver station, I would seriously appreciate it.

Writing unit tests for this would probably be worthwhile too.

I don't have to touch anything else for this to work, right?

Fixes: #35

[ArchdukeTim]

I can test it. Lemme know how

[auscompgeek]

Basically, on your driver console laptop, fire up something that uses pynetworktables, make sure it starts the DS client, and fire up the DS.

I'll most likely add some unit tests once I get around to it too.

[ArchdukeTim]

Oh that mean i need python and git and everything on the DS laptop? Oh boy

[virtuald]

Technically, you could build a standalone pynetworktables2js executable and try it that way...

[ArchdukeTim]

Well I've got a DS here anyway

[auscompgeek]

So I still haven't gotten around to finishing this. But the basic idea for tests is this:

• Create DS client with mock dispatcher
• Start TCP server
• Start DS client
• Wait for connection (with reasonable timeout - 1 second?)

Then, do each of the following (separate tests):

• Send garbage data:
  • invalid JSON
  • valid JSON, incorrect schema
  • two JSON objects concatenated together (this should actually work I believe)
• Send nothing (just disconnect)

Then check the relevant mock methods were called.

[auscompgeek]

Finally took the opportunity to rebase this and clean it up a bit. Still need to write tests (and also probably actually test it works with a real robot too).

[virtuald]

Tested on my real DS and it works. Thanks for this!