Analytic Accounts for Project Tasks

== Purpose ==
When recording time on HR Timesheet, be able to select the specific Project Task where the time was spent.

== Current behaviour (v7) ==
* HR Timesheets allow to record time on Analytic Accounts (an Analytic Account maps to a record),
but it's not possible to link that time to a specific Project Task.
* The `project_timesheet` module allows to record time on Tasks, but it doesn't integrate with HR Timesheets:
a new line on Task Timesheet creates a copy of it on HR Timesheet, but they are not kept in sync; changing the later doesn't update the former; also, creating a line on HR Timesheet also does not have any effect on task Timesheets.

== Proposed Solution ==
* Leave HR Timesheets as they are; time related to Tasks should be recorded on Task-specific Analytic Accounts.
* Instead, each Project Task should have a corresponding Analytic Account, child of the Project's analytic account.
* Add to Project Tasks a many2many link to analytic lines, to use instead of `project_timesheet`.

EDIT: just figured out that this is exactly what the `project_issue_timesheet` module does.
EDIT2: a module to address this already exists: lok at http://bazaar.launchpad.net/~hr-core-editors/hr-timesheet , module "timesheet_task".