"Configure New Name" dialog should explain delay

[JeremyRand]

We should add the following warning to the "Configure New Name" dialog:

The registration procedure will take approximately 2 hours and 10 minutes. You can close Electrum-NMC in the interim if you want, but if you do, you'll need to re-open Electrum-NMC after that duration to finalize the registration. You can see the remaining ETA in the Manage Names tab.

This will avoid user confusion, since many users are accustomed to single-step cryptocurrency protocols (in which operations are near-instant), and have no familiarity with multi-step smart-contract protocols (e.g. Namecoin registrations) where each step must gain confirmations before the next step can proceed.