Fuzzy search with trigram

[dpakprajul]

Issue copied from:
mrmap-community#55

For the fuzzy search, there are some algorithm like levenshtein, soundex, word_similarity and so on.

https://www.postgresql.org/docs/current/fuzzystrmatch.html
https://www.postgresql.org/docs/current/pgtrgm.html

In the mapbender/http/classes/class_metadata.php in line 1284, the code could be change from:
$whereStr .= "searchtext LIKE $" . ($i + 1);
to
$whereStr .= "(strict_word_similarity($" . ($i + 1) . ", searchtext) > 0.2)";

In order to use strict_word_similarity( ) function, we need to install in the postgres first.
CREATE EXTENSION pg_trgm;

Work still need to be done: Check the performance of the search, since a new algorithm is used instead of LIKE.

[dpakprajul]

I think its better to close this issue as it won't go further and has no future. Okay?