Add daemon plugin

[Shelnutt2]

Add support for a daemon plugin which can manipulate a table in order to perform maintenance operations. Initially this will be limited to file consolidation.

Two strategies that need to be examined are having the daemon use the handler interface to interact with the table structure, similar to handler_socket plugin. The second strategy is to link directly to ha_crunch library and manipulate the table outside of mariadb handler structure. The main issue with the second method is locks still need to be acquired in order to safely consolidate the files.

[Shelnutt2]

The latest idea is to just use a background thread to launch the daemon process from the plugin init function. We can then clean up by implementing a de-init function. This needs additional testing to determine the feasibility and the best approach.