Add as(Domain)BareJidString()
Add Jid.as(Bare|Full|…)IfPossible()

Also extend JidUtil with some nice little helper methods.
Add note to XmppStringUtils.isBareJid()

about JidUtil.validateBareJid(String).
Use switch/case in unsecapeLocalpart()
Make JidUtil.withoutResource() more idiomatic
jxmpp-jid: Use CharSequence where possible
jxmpp-jid: Fix typos
Revert "Prevent JID string hash collision attacks"

This reverts commit f912fa359b4db78ead89032df64455f8d65e6398: HashMap
guarantees that it's Keys are not only compared by the hash but also the
equals() method.
jxmpp-jid: Add comment about importance of stringprep order
Stringprep: s/nameprep/domainprep/ s/nodeprep/localprep

Nameprep and Nodeprep are terms from the currently active but soon to be
obsolete RFC 6122. Better to use generic names.