Add ability to close old assets.
Merge branch 'asset-compassion' into 7.0

Add ability to close old assets
Don't mess up with contacts and companies on delete partners
[FIX] Access rules for contract lines
created contract_group class
Some PEP8 in contract_group
Add contract groups in simple recurring contract. Moved invoice generation to contract group class
[ADD] acces rights on contract groups. [ADD] partner_change callbacks on group and contracts. Adapted sponsorship contract customizing to fit new model.
[FIX] headers, PEP8, YAGNI for simple_recurring_contract and sponsorship_compassion
Change simple_recurring_contract to recurring_contract. [ADD] mail.thread on contracts and contract groups.
[ADD] search on child code in contracts, module description, refactored module name
[RM] group checkbox in invoicer wizard. [MV] simple_recurring_contract to recurring_contract [FIX] Generation issue in advance billing
Changed module dependency from 'account_analytic_plans' to 'account_analytic_compassion
My bad... the module should not be dependent for the production or it would install the analytic plans over the already existing data. However in a test environment, we should not forget to install first the module 'account_analytic_compassion' before installing 'sponsorship_compassion'.
[FIX] Contract duplication. contract_group description. Moved fields in contract view. Removed debugging next_invoice_date track_visibility
Added default start date of contract.
New wizard allowing splitting payments. New folder hierarchy inside module. Ability to edit contracts directly from the Reconcile + Put in Fund wizard.
Added contracts modification from Split Payment Wizard.
French translation for module. Updated some texts.
Fixed XML indentation and references to module recurring_contract.