ui: programmatically design all tabs and forms

[tahini]

See #10

Now the forms are half defined in QT designer .ui file and half programmatically (all fields). The result is that widgets cannot be entirely resized or contained in layouts, what works in QT designer does not in QGis. And not all can be scrolled.

QGis also define their own widgets that extend QT widgets, like QgsScrollArea (https://qgis.org/pyqgis/3.4/gui/QgsScrollArea.html), that can be used instead of the base widgets.

Programmatically defining the forms may give us more control in their layout.