Basic responsiveness for mobile devices

[Doru991]

(Requires #45 )
This PR adds a simple 'mobile mode' based on screen width.
In mobile mode, the application is split into two views:

• Menu: Server list, channel list, user list are visible and settings can be accessed (the settings menu is not adapted to mobile yet but should still be usable, although uncomfortable)
• Chat: Other elements are minimized and the chat window fills the screen, with the channel name at the top and chat box at the bottom.
  In order to switch views, we currently have a button near the top at the screen that appears while the application is in mobile mode.

Not all features of the app are adapted yet, but you can navigate servers and channels and chat comfortably.

Tested on:

• Desktop (Window resizing): Works
• iOS (live deployment): Works
• iOS (independent install): Works after fixing bug that broke the application on all platform (P.S. for frontend team: Don't forget to do regression tests and ensure you can build the application and run it in release mode to avoid surprises)