Add support for uninstall

Hey guys,

Glad to see there was an update to this plugin, but can you please add support to uninstall data for those who do choose to uninstall the plugin.

https://developer.www.ads-software.com/plugins/the-basics/uninstall-methods/

Feel free to grab the code from the plugin I made to handle this:

https://imforza.github.io/local-market-uninstaller/

https://github.com/imFORZA/local-market-uninstaller/blob/master/lme-uninstaller.php

https://www.ads-software.com/plugins/local-market-explorer/