[FIX] translate: allow common english 2 chars terms

Before, all isolated (between xml/html tags) two chars words coming from views were not translated (by choice).
But, for some words, allowing them is useful. For instance, the word 'or' located between two buttons.

opw-616716
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64