[16.0][ADD] hr_timesheet_clean module

[acsonefho]

This module lets the user to clean some empty timesheets (for a specific date range). This is usefull when you have a lot of empty entries into timesheets (so visible into analytic accounting) and you want to clear them.

Usefull when someone create entries with this module: https://github.com/OCA/hr/pull/1344