[Code Cleanup/SDK] Updated the example plugin.xml in the SDK.
* [Plugins/SDK] Added an 'example.activity_log.event' plugin to the SDK to demonstrate how to add new Activity Log events.
* [Mail/Parser] The mail parser would previously choose a sender address from either the 'Reply-To:', 'From:', or 'Return-Path:' headers (in that order), but if one turned out to be malformed then the others wouldn't be checked.  Now the subsequent headers will be checked until a match is found.
* [Mail/Parser] The mail parser is now more tolerant of malformed 'From:' headers when processing new messages, and will fallback to a simpler email address search if the personal name doesn't comply with RFC-2822.  For instance, all commas in a personal name should be quoted (e.g. "Last, First" <mailbox@example.com>).  When this wasn't the case, messages were being sent to /storage/mail/fail/.
* [Mail/Parser] Suppressed a PHP Notice in the mail parser when mbstring doesn't support the given encoding.  This doesn't affect message processing in any way.
* [CHD-3673] [Virtual Attendants] Fixed a PHP notice ("Undefined index: _types") in Virtual Attendants when editing an outcome with a 'Worklist Type' condition on a '[UI] While displaying a worklist' behavior.
* [CHD-3670] [Platform/Usability] Fixed the broken 'spinner' image when URL rewriting is disabled.  For instance, when replying to a ticket the "Loading, please wait..." popup should have an animated image.  When the page URLs contained '/index.php/' this image was broken.
* [Mail/Usability] When replying to a message, the 'suggested recipients' will now ignore invalid addresses in the original From/To/Cc headers.
* [CHD-3614] [Mail/Relay/Usability] Worker replies that are received through the mail relay will now have any leading blank lines automatically removed.
* [CHD-3672] [Web-API/Groups/Buckets] Implemented 'GET /groups/123.json' in the Web-API for retrieving information about a specific worker group.  The optional parameter 'expands' supports the following comma-delimited values: 'buckets' (a full list of the group's bucket) and 'members' (a full list of the group's managers and members).  See: http://cerbweb.com/book/latest/developer_guide/rest_api/groups.html#retrieve

* [CHD-3672] [Web-API/Groups/Buckets] Implemented 'POST /groups/search.json' in the Web-API for filtering the full list of worker groups.  See: http://cerbweb.com/book/latest/developer_guide/rest_api/groups.html#search
* [Web-API/Usability] Then performing a 'POST /rest/.../search/' in the Web-API, the '_labels' and '_types' dictionaries are now consolidated in a top-level 'results_meta' key.  Previously these were repeated for every result, which wasted cycles and bandwidth.
6.6.3 checkpoint