Update alert activation improvements

[zorgiepoo]

• Don't activate app when bringing up update alert errors
• Don't set status window level to floating
• Add minimize option to status window after checking for updates (i.e, downloading / installing)
• Allow install button to have focus when app has just launched for scheduled updates within a small threshold (1.5 sec)
• Reset install button focus when app becomes active again for scheduled updates

Fixes #1008
Related to #924

Misc Checklist:

• My change requires a documentation update on Sparkle's website repository
• My change requires changes to generate_appcast, generate_keys, or sign_update

Only bug fixes to regressions or security fixes are being backported to the 1.x (master) branch now. If you believe your change is significant enough to backport, please also create a separate pull request against the master branch.

Testing

I tested and verified my change by using one or multiple of these methods:

• Sparkle Test App
• Unit Tests
• My own app
• Other (please specify)

Tested scheduled updates in regular and backgrounded/dockless apps, at launch and non-launch scheduled times.
Tested bringing app back in background from scheduled updates after it's been running for some time.
Tested status window is not floating for deckless app and is now minimizable.

macOS version tested: 12.1 (21C52)