Release 5.1.0 - documents variants, statistics and ui improvements

[TASK] Add me to the release notes

Merge pull request TYPO3-Solr#383 from timoschmidt/task/release-4.0.x…

…/382-prepare-release

[TASK] prepare release for version 4.0.2

Merge pull request TYPO3-Solr#381 from peterkraume/origin/release-4.0.x

[BUGFIX] fix fallback path of defaultImagePrefix for indicator icon

Set version to 4.0 in

* ext_emconf.php
* install scripts

* Set version to 3.1.2

Fixes bug that wrong index configuration is used when new record was …

…created (Issue TYPO3-Solr#48)

Maintenance Release, fixes composer related issues

Release of version 3.1.0

Created tag for beta release 3.1.0-beta