Better handle prices

[nymous]

When creating an article or a subscription offer, we ask the admin for a price in decimal euros (5.00€), but we save it as cents in the DB (500). This avoids floating point errors when computing.
However because of this duality (form has a price but we save a price_cents), validation errors are hard to surface.

We could use Money and its Rails integration Money-Rails, to handle all the heavy lifting, validation...

[D0gmaDev]

The gem seems to go way beyond what's needed, but I believe it's crucial for lea5 to be reliable as for money, therefore I support @nymous 's proposal.