CA-147941: Fixed the RPU wizard hang in "Reconnecting Storage" and connecting action stuck in progress state

In some cases calling Control.Invoke() from a background thread causes that thread to go in a "sleep, wait, or join" mode, while waiting for Invoke to happen, although the UI thread is running normally.
If the Control is the MainWindow, it works as expected, but we've seen it happening while connecting or disconnecting from a large pool, on calling Invoke on controls like NavigationView, AlertSummaryPage, HistoryPage, etc.
To fix this, we call the Invoke on the MainWindow in all the places where we've seen the issue.

With this changes, the previous fix for CA-148245 (call RequestRefreshTreeView on CacheClearing event) is not needed anymore, so I removed that call.

Signed-off-by: Mihaela Stoica <mihaela.stoica@citrix.com>
Merge pull request #246 from MihaelaStoica/CA-147941

CA-147941: Fixed the RPU wizard hang in "Reconnecting Storage" and connecting action stuck in progress state