Merge remote-tracking branch 'upstream/master' into installeruninstall

* upstream/master: (468 commits)
  Fix error prone warnings (#4290)
  Fix freeze on import into current library (#4299)
  Upgrade gradle to 4.10 update xmlunit and postgres
  update xmlunit-matchers from 2.6.0 -> 2.6.1
  update gradle build-scan from 1.15.2 -> 1.16
  checkstyle
  execute changes only if disk db present
  Fix Export to clipbaord action (#4286)
  fix npe in Merge entries dialog
  Add minimal height for entry editor (#4283)
  Fix exceptions when trying to change settings (#4284)
  Added a comment for the purpose of the class (#4282)
  Fix NPE when importing from CLI (#4281)
  Fix display of key patterns
  convert bibtexkeypatterndlg to javafx as well (#4277)
  Style preference sections using css
  Fix a few style issues
  Changed the behavior of the field formatting dialog (#4275)
  Fix checkbox display
  Remove small font size
  ...

Author: Siedlerchr

.travis.yml

@@ -60,6 +60,7 @@ after_failure:
 branches:
   only:
     - master
+    - maintable-beta
 
 # cache gradle dependencies
 # https://docs.travis-ci.com/user/languages/java#Caching
@@ -70,3 +71,4 @@ cache:
   directories:
     - $HOME/.gradle/caches/
     - $HOME/.gradle/wrapper/
+