Improve concurrency and performance of conversation log history.

OF-1746: Add option that allows certificate revalidation to be skipped (client)

OF-1539: Negative caching for groups.

This builds on the solution introduced in OF-1631 and the fixes for OF-1589.

* Make sendMessageToAdmins async to speed up node loss notifications

* a) Ensure we cache names of nodes that are already in the cluster
b) Log the name of the senior cluster member

* Include occupant nickname in MUCEventListener.occupantLeft to mirror the metadata passed to MUCEventListener.occupantJoined.

* MucEventListener.occupantLeft - provide default methods to support older clients without nickname and mark the old method as deprecated. Update javadoc.

OF-1774 CleanupTask did not remove empty rooms in clustered environment.

OF-1640: Better protect against rogue responses

OF-1772 Enable configurable kick reasons for admin console + timeouts

OF-1647: Rename the legacy WEB-INF/lib folder on startup

OF-1747: Update to Rome 1.12.0

OF-1748: Update to log4j2 2.11.2

OF-1749: Update to Guava 27.1

OF-1750: Update to MS SQL Server JDBC Driver 7.2.2.jre8

OF-1751: Update to commons-codec 1.12

OF-1752: Update to commons-file-upload 1.4

OF-1753: Update to JAXB API 2.3.1

OF-1754: Update to Jaxen 1.2.0

OF-1758: Update to commons-dbcp2 2.6.0

OF-1759: Update to commons-lang 3.9

OF-1760: Update to commons-fileupload 1.4

OF-1762: Update to commons-pool 2.6.2

OF-1763: Update to httpclient 4.5.8

OF-1764: Update to awaitility 3.1.6

OF-1765: Update to Bouncy Castle 1.61

OF-1766: Update to jSMPP 2.3.7

OF-1767: Update to Mockito 2.27.0

Update maven plugins

OF-1761: Update to JavaMail 1.6.2

httpbind: Improved Logging / Diagnostics

* OF-1727: Update to Jetty 9.4.17.v20190418

* OF-1727: Update to Jetty 9.4.18.v20190429

OF-1768: Fix Javadoc errors (NB. No code changes)