ExchangeMarket

• Full rewrite of the plugin. Moved order handling away from the db handler and into the command classes.
• DB structure remains the same, orders from older versions will work fine.
• Added support for sqlite, on by default.
• Commit command doesn't just reissue the same command again, buy/sell commands save the orderID and amount and commit pulls only from those orders, prevents price from changing between buy and commit command.

* Single threaded, may lag server.
* Will default to sqlite on first run, servers running pre v1.1.0 need to set db-type to "mysql" in the config.