Fix id.blockstack name registration

[markmhendrickson]

When I try to register a name for my newly registered ID, I get the following hanging error (shown in console) even when trying different names:

[yknl]

@markmhx you've hit the free name registration limit. The error handling could be improved though.

[markmhendrickson]

@yknl How does the current limit work? (i.e. maximum names, time factor if any)

[yknl]

The subdomain registrar limits names registered by IP address. I don't have the number on hand. There's an existing issue to add an admin interface on the registrar to reset the limits here: stacks-network/subdomain-registrar#19

[markmhendrickson]

@aulneau I've added this to the new sprint with your assignment