Add basic automated script

Quoting the last commit:

While the performance framework was originally written to collect
performance metrics, driving the shell by an automated script is
also useful to ensure that basic functionality is working.

Add such a basic test, initially checking top bar menus, notifications
and the overview.

The idea is to combine this with !1349 (merged) to have a more elaborate (and easier to extend) test case than opening the overview view the D-Bus Eval() method.