(cherry picked from commit 78c98bc)

* Fix fetcher tests

remove uncessary logging in l10n which makes fetcher test fail

ISBN tests still fail both
Fix arxiv tests, eprint now has url in front

* rework fetcher tests
Fix logging configuration
Fix eprint field of arxiv
Return empty results when 404 or 400 encountered
Add logging in that case

* fix checkstyle

* match both https and http prefixes in arxiv

* inline prefs in setup method

* fix ebook.de test record, as there is a new version of that book entry

* move comment

RichTextFX will no longer be maintained
FXMisc/RichTextFX#768

* update mockito

* update archunit and errorprone

* fix typo

* Replace old fetcher stuff in command line interface

* Remove cli output

* Make help file optional

* Rework web search pane in javafx

* Show web search and group panes by default

* Use better binding and init default fetcher in view model as it should be

* remove obsolete l10n keys
set search button to default so search can be executed by hitting enter

* fix wrong string util class

Adapt the url of returned data

* Make attached files relative to the file directory

Fixes JabRef#4201
Open files with default OS application if no External file type is present

* add changelog

* use method from linked files view model for linked file

* fix opening of file from menu
add monadic binding

* fix variable name

* Fix importer vulnerability
Fixed issue JabRef#4229  where importer was vulnerable to XXE attacks by
disabling DTDs along with adding warning to logger if features are
unavailable. fixes JabRef#4229

* Fix minor code errors and logger optimization
Removed author line in class comment. Reworded CHANGLOG.md. Set
DTD features to individual final static constants. Optimized
logger by parameterizing feature and error.

* Rearrange import statments for project compatibility

* Remove merge artefacts from changelog

# Conflicts:
#	build.gradle

(cherry picked from commit 8dce805)