Using `sale_product_matrix`'s tour as `product_matrix` doesn't
actually have any test for this.
Remove t-raw from the product_matrix(.extra_price) template, by moving
the formatting to the client side (unclear why it was done by the
server in the first place).
Also fixes a bug where a negative price_extra would have *two* `-`
signs: one before the currency, and one after the currency: the price
being formatted should be abs'd to avoid a negation being generated by
the monetary formatting. Also uses non-breaking spaces everywhere
where the server-side formatting mixed breaking and non-breaking
spaces. Keeps from the original the peculiarity that the extra price
should always have a sign positioned before prefix currency signs.
Also changes the calling conventions of `product_matrix.extra_price`:
instead of being called with a formatted `price` it's now called with
the entire cell object.
Xavier Morel