Add Credit Offer page next to pools

[sschiessl-bcp]

Implement first version as seen on https://develop.bitshares.org/#/credit-offer

Target layout is like pools page, and add a column that directly shows the offered price for the collateral. This could e.g. be multiple rows in one cell for each allowed collateral.

Backend call is https://api.bitshares.ws/docs#/openexplorer/route_creditoffers_openexplorer_creditoffers_get