[FIX] base: guess_mimetype
[FIX] base: guess_mimetype

When receiving an email containing two attachments(.docx, .odt) with the chatter
the icons displayed for the two attachments were the icon of a zip file instead
of the icon of a document file.

ps: the dictionnary "mapping" with the mimetypes and the signatures has been
changed in a tuple of tuples to keep the order of the mimetypes because
all the document files (.docx, .dot) begin by 'PK\x03\x04' and all the
zip files by 'PK'.

opw:658706

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