Merge remote-tracking branch 'origin/bitfireAT/master'

# Conflicts:
#	.gitlab-ci.yml
#	build.gradle
#	src/main/java/at/bitfire/dav4android/DavAddressBook.kt
#	src/main/java/at/bitfire/dav4android/DavCalendar.kt
#	src/main/java/at/bitfire/dav4android/DavCollection.kt
#	src/main/java/at/bitfire/dav4android/DavResource.kt
#	src/test/java/at/bitfire/dav4android/exception/HttpExceptionTest.kt