* Improve login process with newer APIs
* Implement login with WebView instead of browser tab or external browser
Oauth process requires us to open login prompt for correct instance and
we need to receive the result back. Usually it is done with redirect
parameter.
Previously we've been using BrowserTabs API and have been falling back
to just opening browser. This mostly worked but is very clumsy:
- It relies on few system mechanisms for opening URLs in both
directions
- Browsers do weird things and tend to break quite a bit
- There's a good chance that the app can die in the process and we need
to recover our state.
So instead we are now using WebView. It has disadvantages (users have
to trust us to show correct page, logins are not shared w/ browser) but
it should be more reliable.
* Changes to login after review
* Move login classes to their own package
* Fix linting issues
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