add the possibility to reload the TAP schema

[vforchi]

I would like to be able to reload the TAP schema mappings without having to initialize the servlet. I was thinking of reinitializing TAP.service.metadata, but that field is private and final, so it is clearly not desired by design.

The reason behind this is that we have automated procedures that add new catalog (tables) to the schema, and we would like to be able to make these new table available to the server without having to kill existing queries.