Add support to search providers (fix #79)

To wrap up changes:

 * Default provider is just a bare-bones-search-in-mysql-using-like
 * Support ElasticSearch for a faster search
 * Create a console to setup, initialize and clear a search provider
 * Adjust *handlers*, models, tests, worker, etc. to changes
 * Create some config entries
 * Update docs (re #19)

Thanks @luizgpsantos for the support :+1: