Retry in-app verification before failing

[keeshux]

StoreKit is unable to report failures and may occasionally return empty products instead. This is a mitigation attempt to avoid "Purchase required" for legit paying users.

Relax tunnel verification parameters:

• Verify after 2 minutes
• Repeat verification every 6 hours
• On failure, retry after 5 minutes
• Fail verification after 3 failed attempts (2 + 3 * 5 = 17 minutes grace period)

Relax app verification frequency:

• Do not always reload the receipt on foreground, thus invalidating the current one
• Invalidate current receipt after 10 minutes

Fixes #1312

[keeshux]

Observations:

• Raise verification interval to 1 day maybe
• Graceful period after first failure
  • First verification after 2 minutes
  • Retry 3 times
    • After 1/2/5 minutes (8 total grace)
    • Change alert to say (delay + grace) minutes = 2 + 8 (not just delay)