Add name functionality to QML GUI

[JeremyRand]

Upstream Electrum has switched their Android GUI from Kivy to QML:

https://github.com/spesmilo/electrum/tree/1880c6a74987ad602914a851c54f364c740e900b/electrum/gui/qml

Coincidentally, upstream Bitcoin Core is doing experiments with switching their desktop GUI to QML as well:

https://github.com/bitcoin-core/gui-qml/tree/e7bea2d9373764427878531b66e246c4ba94235f/src/qml

It would be highly desirable to implement name functionality into Electrum-NMC's QML GUI, keeping in mind the possibility of porting it to Namecoin Core later. That means sharing as much code between Electrum-NMC and Namecoin Core as possible, just like we do currently with Electrum-NMC's Qt GUI and Namecoin Core's Qt GUI.