Prepare for Search API Solr 4.3/ deprecate hooks

[DiegoPino]

See esmero/format_strawberryfield#293

See https://www.drupal.org/docs/8/modules/search-api-solr/search-api-solr-howtos/how-to-replace-the-deprecated-hook-hook_search_api_solr_query_alter-with-prequeryevent

This implies:

• Testing if Search API Solr did not break more stuff (it might)
• Move the hooks to event subscribers.
• Change dependencies to 4.3 or higher (older won't work bc the classes needed for the event are not present)
  All our Solarium/query alters are in the main module file

[DiegoPino]

Resolved. We only use events since 1.2