Cmis read

Port of https://code.launchpad.net/~savoirfairelinux-openerp/knowledge-addons/cmis_read/+merge/212260

Add cmis_read; It allows to use the CMIS backend to search in the DMS repository
and attach documents to OpenERP records.

LP reviews
--------------
* @max3903: Approve on 2014-06-19 
* @bwrsandman: Approve on 2014-06-19
* @guewen:
    > Hi,
    > It seems nice.
    > I left a few comments in the diff. I won't really block on them but you should have a look.

@guewen:
> The size is not mandatory and should be used only when it is a constraint.