* Distinction and interaction between service class and server object
          o Common server properties like id, name, machine name, etc., are now only stored in the server object.
          o The service object has now a defined constructor, which contains the corresponding server object as a parameter.
          o The abstract service class saves $server and a reference to $server->options (as $options) in its constructor.
          o When a service class wants to access other server properties (apart from its own settins), e.g. the server ID, it should just use $this->server->id.
    * Service configuration form handling
          o The signatures of the three SearchApiServiceInterface::configurationForm*() methods have changed.
          o $prefix is gone, simply use form_error() instead.
          o SearchApiServiceInterface::configurationFormSubmit() has a new purpose, as it is now responsible for storing the new service options itself. This is most easily done (when extending the abstract service class) by setting $this->options appropriately.
          o If you haven't overridden these methods, you can ignore these changes – the abstract service's default implementation works just as before.
    * Renamed SearchApiServiceInterface::view() to SearchApiServiceInterface::viewSettings().

Documented Entity API special properties "module" and "status".

Some other small changes and additions.

Main results:
- Completed search_api_db module.
- Added HTML filter preprocessor.
- Wrote tests.
- Several bug-fixes, etc.