[DOC] mail: add some docstrings for mail context keys
[DOC] mail: add some docstrings for mail context keys

Too much keys kills keys. Difficult to say.

syci/OCB,laslabs/odoo,dfang/odoo,storm-computers/odoo,sysadminmatmoz/OCB,dfang/odoo,dfang/odoo,stephen144/odoo,optima-ict/odoo,laslabs/odoo,optima-ict/odoo,bplancher/odoo,syci/OCB,bplancher/odoo,bplancher/odoo,storm-computers/odoo,microcom/odoo,storm-computers/odoo,ygol/odoo,sysadminmatmoz/OCB,hip-odoo/odoo,dfang/odoo,Elico-Corp/odoo_OCB,storm-computers/odoo,hip-odoo/odoo,sysadminmatmoz/OCB,sysadminmatmoz/OCB,ygol/odoo,Elico-Corp/odoo_OCB,syci/OCB,syci/OCB,bplancher/odoo,storm-computers/odoo,syci/OCB,optima-ict/odoo,hip-odoo/odoo,laslabs/odoo,dfang/odoo,ygol/odoo,ygol/odoo,laslabs/odoo,syci/OCB,microcom/odoo,optima-ict/odoo,sysadminmatmoz/OCB,microcom/odoo,stephen144/odoo,laslabs/odoo,laslabs/odoo,sysadminmatmoz/OCB,optima-ict/odoo,stephen144/odoo,microcom/odoo,hip-odoo/odoo,ygol/odoo,ygol/odoo,Elico-Corp/odoo_OCB,Elico-Corp/odoo_OCB,microcom/odoo,Elico-Corp/odoo_OCB,dfang/odoo,hip-odoo/odoo,storm-computers/odoo,bplancher/odoo,ygol/odoo,Elico-Corp/odoo_OCB,stephen144/odoo,optima-ict/odoo,stephen144/odoo,sysadminmatmoz/OCB,microcom/odoo,hip-odoo/odoo,bplancher/odoo,stephen144/odoo