Update to QML

[Jzarecta]

Been going through the code for a while, and I think the way to make it the wallet easier to contribute is if we start replacing Qt widgets with QML or Qt Quick controllers that allow the better design of the interface without deep knowledge of Qt or C++.

One of the things that we can start is for example with the QtTableWidget with the QML TableView type. Same with the forms for sending and receiving coins, this will make it more easier to style it, and better mantainability.

[Jzarecta]

Some info about QML that I wrote a few weeks ago. Referencing a point of sales. https://steemit.com/programming/@jza/qml-point-of-sales-can-we-use-this