Refactoring on the settings needed to implement settings page

Ref #185 (closed)

Those are the changes needed to implement the actual settings pages of the MR !212 (merged)

It creates a separated goroutine that si responsible for writing data in the database (meta.Runner), where all requests to store data are done asynchronously.

Now values can be inserted via meta.AsyncWriter and read using the usual meta.Reader

It breaks the settings package, and suggests that it might not be needed, which means that soon we can get rid of it.