loleaflet: configurable dimming timeout and fire event

Two timeout are now configurable.
idleTimeoutSecs, which controls when to dim because
of user inactivity, even if the tab is in focus.
outOfFocusTimeoutSecs, which controls when to dim
when the tab loses focus.

Currently they are set to 15 minutes and 30 seconds
respectively by default.

User_Idle event is now fired on dimming.

Change-Id: I894f6df44825b6814872f1c4986fab8dcd4d6cef
Reviewed-on: https://gerrit.libreoffice.org/37373


Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>
Tested-by: Ashod Nakashian <ashnakash@gmail.com>