Better pagination in bc-table

So modelChanged() gets called any time anything in the table changes (header, model, config, etc). Any time we are using the exchange pagination style for paging, the code in this TODO is gonna get re-run, and currentPage is always going to be reset back to 1.  (So if you are in a list view, you page to page 10, then the web socket pushes a new model and your table data gets updated, the table kicks you back to page 1)

That happens because this scope.config.pagination.currentPage value is never updated at any time in any bc-angular-directives or buttercoin-web-auth code.