Fix library access error at BasePanelTest

[koppor]

Refs #5602

• hamcrest wasn't visible --> add it to the test dependencies
• refine comments on JabRefLauncher and JabRefMain

I could not fix following issue when executing the test in IntelliJ

ARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by net.bytebuddy.description.annotation.AnnotationDescription$ForLoadedAnnotation (file:/C:/Users/olive/.gradle/caches/modules-2/files-2.1/net.bytebuddy/byte-buddy/1.9.10/211a2b4d3df1eeef2a6cacf78d74a1f725e7a840/byte-buddy-1.9.10.jar) to method com.sun.javafx.beans.IDProperty.value()
WARNING: Please consider reporting this to the maintainers of net.bytebuddy.description.annotation.AnnotationDescription$ForLoadedAnnotation
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
--- Exception in Async Thread ---
java.lang.reflect.InvocationTargetException: null
	java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	java.base/java.lang.reflect.Method.invoke(Method.java:567)
	org.testfx.framework.junit5.ApplicationExtension$AnnotationBasedApplicationFixture.start(ApplicationExtension.java:158)
	org.testfx.framework.junit5.ApplicationAdapter.start(ApplicationAdapter.java:37)

[koppor]

Regarding travis. Only CodeCov is failing - refs #5618

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.

Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received

[Siedlerchr]

Can't we put codecov in allowed failures?

[koppor]

Because of #5609 (comment), it was reenabled. We can discuss it at #5618, where I reenabled codecov failure