Merge pull request #213 from sortega/refactor_protobuf

Reduce currency redundancy in protobuf messages
Fix a bug on ITs

The price was mistaken by the actual amount to exchange so the fixture
was provisioning an insufficient amount of funds.
Merge pull request #215 from sortega/fix_it

Fix a bug on ITs
Fix wrong assertion on OpenOrdersTest

The expected value was a fiat amount while the correct result was
a price.
Merge pull request #216 from sortega/fix_it

Fix wrong assertion on OpenOrdersTest