Improvement: Messages shall not be shown on iPhone main menu

[wutschel]

Description

This PR blocks showing warning/error messages (aka "toaster messages") while the main menu is shown on iPhone. The iPhone main menu is shown in case the centralself.slidingViewController shows its underLeftController, which can be checked by self.slidingViewController.underLeftShowing. This avoids that the user cannot enter the server connection view from main menu while the server cannot be connected and throws error warnings.

Screenshots:

Summary for release notes

Improvement: Messages shall not be shown on iPhone main menu

[kambala-decapitator]

toaster messages

toast messages :)