Migrate fultlext search from Lucene to PostgreSQL

[koppor]

Currently, JabRef employs two different search backends: PostgreSQL and Apache Lucene. PostgreSQL is used for the search within the library (.bib file) and Apache Lucene is used for the fulltext search of PDF files.

It turned out that it is really hard to get "contains" search working properly in Lucene.

the query must be tokenized using the same tokenizer as during indexing to extract words from the query and look into the index for these words.

This will fix JabRef#235.

Working on handling following variants for the same word is as hard in Postgres as it is in Lucene:

• Düsseldorf
• Duesseldorf
• D\"{u}sseldorf
• Dusseldorf