Added user survey, community links and fixed all deprecations warnings
This pull request mainly add a user survey dialog that it'll be used to better understand our user base.
We want to collect some basic remmina preferences, like which protocol are used, just to better focus on our development priorities.
None of the collected data will be used for any other purpose (the php source code is available on request)
Beside the survey, I have added and modified our main community links in the Help menu and fixed some different issues like deprecations warnings, code cleaning (glib coding guidelines applied where possible), etc