Fixed fat-finger limits and incorrect error string handling;  Fix to OrderSubscriptionManager for case of legitimate disconnection;

CHANGED: Trading.aspx.cs
-- Now pulls in trading and viewOnly accounts.
-- Additional logging for case of zero rows returned for data tables.
-- DataTables now tolerate nulls for case of zero rows returned.

CHANGED: UserAccountManager.cs
-- Now checks with AccountManager to see if accounts are existent.

CHANGED: OrderSubscriptionManager.cs
-- Added handling for the case where messages arrive when the client is
   legitimately disconnected, ie being serviced, rather than just timed out.
-- Renamed variables accordingly.
-- Additional logging.
-- Improved string handling for repeated pipes, using Regex.

CHANGED: Order.cs
-- Fixed problem with string error, should have been a reference.
-- Fixed problem with IsNumeric(), now removed and using TryParse().
-- Improved error messaging when price is non-tick, to show tick size.
-- Fixed problem with fat-finger limit check, incorrect comparator.
-- Improved error messaging for fat finger limit breach.

CHANGED: MarketManager.cs
-- Added CloseMarket()
-- Improved handling of multiple pipes in error messages, using Regex.

CHANGED: MarketDefnDAL.cs
-- Tolerates incorrect ordering of Max/Min price limits.

CHANGED: MarketDefn.cs
-- Tolerates expiration time in the past, warns, and suggests soft delete.

CHANGED: Market.cs
-- Minor changes to strings returned.

CHANGED: AccountManager.cs
-- Added IsValidKey() to return true if key is contained.

CHANGED: .gitIgnore
-- Ignore XLS and XLSX files.

ADDED: OrderTestData.SQL
-- MySQL flavoured data for testing.