[FIX] web_graph: pass context to fields_get for translation

In graph views, fields from the pivot table were not translated in the user language
We pass the context, containing the user language, to fields_get in order to get the translation
This is also done by the search view, in search.js line 1978 at this rev.

opw-616713
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64