Revert "[ADD] purchase: average price computation test"

This reverts commit 5f9280e854ac435bdcf903128d5e9d5d0b592070.

These tests have been introduced in 7.0/saas-3, but can no longer be applied in 8.0, as they uses models that do not exist anymore in the new wms.

if such tests do not exist yet in Odoo 8.0, then these tests needs re-work, they cannot be applied like that

Conflicts:
	addons/purchase/tests/test_average_price.py
[FIX] res.currency: correctly compute the number of decimal places for currencies formatting in 'get_format_currencies_js_function'.
[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
[FIX] sale: rounded sales team invoiced gauge

The price_total field of the account invoice report is not rounded (it cannot be easily rounded, as this has to be done in the sql view)
In a multi currencies environment, this is possible that the price_total value has a lot of digits
We therefore round it manually, for the gauge of the sales team kanban view
[FIX] Use _unknown model for missing models in relation fields

During a migration of database, it is possible that some custom field
("x_", state is 'manual') are relational to model from a module that is
not provided.

Note: this used to work in Odoo 7.0 but crashed in 8.0.

Closes #3877
Merge remote-tracking branch 'odoo/8.0' into 8.0