api: bug fix: correct http codes for errors
connected middleware with meta data repository
client: display errors from the server to the user
client: made raw query functional
server: exposed raw queries through the API
marc21 adapter: bugfixes
client: add html links to sources for raw query
marc21 adapter: bugfix
server: removed some debug code...
marc21 adapter: validate configuration on creation
marc21 adapter: bug fix wrt error handling
marc21 adapter: improved configuration validation