RcFile: simplify creation of UI files

[narnaud]

THis is a big change to simplify the creation of ui files from rc files, and fix some issues:

• add API for QtUiDocument for writing data (add widgets, properties....)
• remove the rc2ui.js script for ui creation from rc files
• avoid having duplicate ids in the same dialog (it's a mess for later)

Fix #42

[narnaud]

Also fix #43