removed AdServerConnector class
    AccountSummary: renamed "available" to "balance"
    AccountSummary: removed lineItems, adjustment* and allocated
    json_listener: added request accounting and "/stats" request
    moved PostAuctionEvent and SubmittedAuctionEvent in common/
    added unit test that ensures the values of AccountSummary are consistent with those of the underlying accounts
    replaced impression/click events with equivalent campaign events
    removed doVisit and related functions from PA loop