Improve experience when gcalcli is missing auth

[dbarnett]

Should give more user-friendly output about auth issues after fresh install (and probably when auth becomes expired/invalid, too).

If you just install gcalcli and invoke gcalcli list with no prior setup, it seems to point you straight to an authentication link that no longer works and says "App is blocked". This could be way less error-prone.

Also, it seems to require separate authentication for calm/calw vs. list, but doesn't seem to explain that anywhere obvious. That could be clarified and have the experience improved, too.

[dbarnett]

And also if you haven't used apps with similar auth setup before, it's not super obvious that (at least in Chrome) you need to proceed past the scare page by expanding an "Advanced options" thing and selecting "Proceed anyway". Could use hints about that.

[dbarnett]

Oh and related to the "and probably when auth becomes expired/invalid" part, people seem to get stuck needing to manually delete and force refresh authentication (example: #682 (comment)). Would be nice if gcalcli were more self-aware about those invalid auth cases and more helpful about what to do about it.

[dbarnett]

K, I think I got all of those different smells improved!

1. "it seems to point you straight to an authentication link that no longer works" -> removed in Improve auth setup experience with more self-contained explanations/links #707
2. "it's not super obvious that (at least in Chrome) you need to proceed past the scare page by expanding an 'Advanced options' thing" -> Also fixed in Improve auth setup experience with more self-contained explanations/links #707
3. "it seems to require separate authentication for calm/calw vs. list" -> can't repro and can't find any reason from the code it'd be like this, must've just gotten something mixed up
4. "people seem to get stuck needing to manually delete and force refresh authentication" -> improved in e459ca7, so if you just run gcalcli init, you'll be prompted for whether you want to manually refresh auth.