jami-client-qt

The bug is caused by the computation of `elementWidth` when the list
model length is zero and `showWindows` is true. In this case, division
by zero causes the `elementWidth` to have the value `Infinity`. We
presume that at this point, the component's rendering may take a
while.

This commit refactors the layout to use a GridLayout and a more stable
approach to displaying the delegate components, while removing a
potentially harmful Qt bug [1] workaround.

[1]: https://bugreports.qt.io/browse/QTBUG-110323

Gitlab: #1242
Change-Id: Ib3df1568fdbcdd799fcdcf0b39cb87e3de50dc42