[Fix JENKINS-22536] Use ISO 8601 date format for GitChangeSet dates

The date format presented previously was a combination of the ISO 8601
formatted date and a copy of the time zone information from the original
git change log entry.

The new format is only the ISO 8601 formatted date, since it already
includes time zone information.
Merge remote-tracking branch 'upstream/2.2.x' into 2.2.x-iso-8601-date-format
Merge remote-tracking branch 'upstream/2.2.x' into 2.2.x-iso-8601-date-format
JENKINS-25048: Added filters check for notifyCommit event
Merge branch 'commitNotify' of https://github.com/pbaranchikov/git-plugin into 2.2.x-pbaranchikov-commitNotify

Conflicts:
	src/test/java/hudson/plugins/git/GitSCMTest.java
Merge remote-tracking branch 'upstream/2.2.x' into 2.2.x-iso-8601-date-format
Merge remote-tracking branch 'cache/2.2.x-iso-8601-date-format' into 2.2.x-iso-8601-date-format
Merge remote-tracking branch 'centos7x64/2.2.x-iso-8601-date-format' into 2.2.x-iso-8601-date-format