Edit lock also pops up during user input, interrupting the typing

[sebix]

Received as a user feedback:

During typing, the edit lock warning popped up, and some user input was lost until the user noticed the popup.

Maybe the lock should be automatically extended when the user is actively typing?

[RogerHaase]

To mitigate the problem with existing code:

1. increase the lock time in wikiconfig.py: edit_lock_time = 20 # minutes, resets when the Preview button is clicked
2. tell user to frequently use "Preview" function to save current state of item, user will get flash message to resume edit at point of last preview if power is lost