Better error-messages for trades

Improved error messages for trades.  Also added an experimental fix for https://github.com/Jessecar96/SteamBot/issues/598
They can be treated as errors after 2 or 3 retries (see the Steam code).

The switch block: switch (tradeStatusType) { ... }

... but looking at the Steam code again, it looks like they only reset the counter (g_cTradePollFailures = 0) when the trade status is 0 (or when rgNewTradeStatus.me or rgNewTradeStatus.them is set).