Fix view margins and layouts

Firstly, container widget in C++ doesn't need any extra padding, as
those are already provided by the tabview.

Next, CheckBoxes in ColumnLayout need to "fillWidth", so they wrap
nicely instead of truncating or forcing layout to stretch (and thus
stretching other fillWidth children).

Then, the classic `if (background)` guard for ScrollView framed styling.

Last but not least, use some Layout magic and appropriate margins &
spacing to replace anchors in Flickable (TableView) in order to fix
that right side of table content went under the vertical ScrollBar.