Improve handling of Server issues/disconnected

[nickvergessen]

During the team week we discussed various improvements that can be done on various clients

• "Connecting / Loading" 3px bar at the top of conversation list or top bar, when starting 🖱️🖌️🍎🤖
• Tiny information when no internet connection 🖱️🖌️🍎🤖
• Tiny information when server is 502 (turn of server) or 503 (maintenance/update) 🖱️🖌️🍎🤖
• Tiny information when server is slower than usual 🖱️🖌️🍎🤖
  • Admin disable option
  • Median over as many days as we can hold
• Dashboard when first loaded is completely empty and should say "Server not reachable" 🖱️🖌️
• Don't offer "Delete account" as first option (when not reachable since recently) 🤖 Remove/improve modal when server is down talk-android#5038
• Inform when scrolling to the top and reaching the end while still not connected 🖱️🖌️🍎🤖