Fix selecting from Elasticsearch with conditions

[peterpp]

Query type "filtered" has been depraceted and is unsupported in current Elastic version. "bool" query has to be used instead. This pull request:

• fixes searching
• adds "must", "should", "must_not" conditions
• fixes searching in system "_id" field
• displays real error retuned by Elastic instead of general "Invalid credentials."
• remove empty body from requests that don't support them (7.14 compatibility)

[peterpp]

I rebased this branch onto field-priviledges (https://github.com/vrana/adminer/pull/422)

[cweiske]

Displaying the real error is indeed a problem with 4.8.0. I get "invalid credentials" for every error.