deprecation: Improve the deprecation notice

[borisyankov]

Makes the app notice more user-centric. We are making it more clear
this app will soon no longer be available.

[gnprice]

This text looks good! I have a few suggestions for further improvement in this interaction:

• Let's say something about how to get in touch with us; perhaps "file an issue on github.com/zulip/zulip-mobile".
• For the onclick handler that is meant to link to the Play Store, let's follow the recommendation in upstream docs:
  • Follow the URL pattern there -- so no hl query-param.
  • Add intent.setPackage("com.android.vending"), so it actually goes straight to the Play Store app.
• For the text of the buttons:
  • "Ignore" rather than "Cancel" -- this is something we're bugging them about that they can ignore for now, not something they've requested.
  • "Update" isn't good because that's the normal term for getting a new version of this app. Better would be something about "install", perhaps "Install new app".
  • I'm dubious of the "ignore permanently" logic that the "Don't show again" button provides -- there's basically no scenario where that's a good experience, compared to reminding again in a week or a month. But the total number of users still on this app may be few enough it's not worth adding new logic for that.

Also the CI failed, saying something about lint. I haven't tried to look into it, and haven't worked with this codebase so I don't have any context on that, but hopefully it's easy to just fix.