Add option to remove tickler command sub-labels on error
Add option to remove tickler command sub-labels on error

This is useful for email clients that do not display the labels applied to a message, or make it easier to add labels than to remove them.

From the associated issue https://github.com/rosulek/gmail-tickler/issues/10:

> While some users might prefer to see the labels that were in conflict, most of the time I can easily remember/re-decide until when I want to snooze the thread. The current behavior is particularly frustrating on email clients (such as Outlook on iOS) that don't show the labels that a thread currently has. If I snooze a thread to time A, and then a new email in that thread bumps it back to my inbox, then I may snooze it to time B without realizing that it already has the label for time A. This will cause it to mysteriously appear in my inbox again and again, no matter how many times I try to snooze it. If the Tickler removed the conflicting labels, then the snooze would again succeed the third time.

rosulek/gmail-tickler,lehrblogger/gmail-tickler,lehrblogger/gmail-tickler,rosulek/gmail-tickler