Rename dx "https" plugin

[awrichar]

As discussed on #202 in relation to tokens, the name "https" is too generic for a plugin.
A plugin not only implies a particular protocol (or protocols), but also a very specific set
of methods and events implemented on that protocol.

The dx plugin should also be renamed - possibly something like "ffdx" or "ffdata"?

[peterbroadhurst]

My thought would be:

• ffdxapi_v1
• fftokenapi_v1