[Code Cleanup]
* [Activity Log/Usability] Fixed an issue where some Activity Log entries were still being created with hardcoded actor permalinks.  These are now generated using a dynamic format which will adapt if Cerb is moved to a new base URL.
* [Activity Log/Migration] Fixed an issue in the 6.0.0 migration script where knowledgebase articles referenced in the Activity Log weren't converted to the new ctx:// URL format.
* [Activity Log/Migration] Fixed an issue in the 6.0.0 migration script where a query attempted to retrieve *all* of the Activity Log entries as a single resultset in order to convert them to a new format.  This could overwhelm the available PHP memory_limit and prevent an upgrade from completing.  These records are now broken up into chunks of 5,000 rows.
[Code Cleanup]
* [Workspaces/Migration] Fixed an issue from the 5.6.0 migration script where certain ticket worklist filters weren't fully converted to their newer counterparts.  This resulted in worklists with nameless filters on them which didn't filter as expected.  While these could be cleaned up manually after the upgrade, some Cerb instances have hundreds of worklists and this process would be tedious.  These rows will be converted properly for people migrating from a version earlier than 5.6.0, and the rows will be fixed retroactively for any later versions by the 6.5.4 upgrade script.
* [Development/POP3] Added a script to /install/extras/developers/ for running a mock POP3 server in order to debug esoteric issues (like sporadic 30+ second connection timeouts).  These conditions are harder to simulate with a live mail server.
6.5.4-dev checkpoint
Merged 6.5.4 into 6.6
* [Virtual Attendants/Migration] Fixed an issue in the 5.4.0 migration script where Group Inbox Routing rules were not properly converted to Virtual Attendant group behaviors if there was only a 'To/Cc' condition.
* [Virtual Attendants/Migration] The 5.4.0 migration script will now create separate 'To:' and 'Cc:' header checks when converting Group Inbox Routing 'To/Cc:' rules to Virtual Attendant behaviors.  Previously it just created a 'To:' header check.
* [Update/Plugin Library] Fixed an issue in 4.x and 5.x migrations where the Plugin Library attempted to download its updates before the 5.7.0 patch created its database tables.  This didn't interrupt the upgrade process, it just logged an error.
6.5.4-release checkpoint
Merged 6.5.4 into 6.6
* [Mail/Parser/Localization] Cerb will now use the 'iconv' PHP extension if it is loaded. This is capable of converting a wider range of encodings than 'mbstring'.  For instance, TIS-620 (Thai) and WIN-1258 (Vietnamese) were not properly converted to Unicode by Cerb when only using mbstring.
* [Mail/Relay] Workers can now manually relay specific messages to external email accounts without having to set up a Virtual Attendant behavior first.  The reply menu on each message contains a new 'Relay to worker email' option.  Selecting the relay option displays a popup where worker email accounts can be filtered and selected.  This feature is particularly useful for situations where workers may need to reply while offline, such as during transoceanic flights or cruises.  A worker can relay messages from Cerb to their mobile email application, reply at their leisure, and their messages will be delivered when network access is restored.  The feature is also useful when certain workers handle requests through email without logging into the Cerb interface (e.g. temps, interns, consultants).  A human dispatcher can route messages to these workers on an as-needed basis.
* [Mail/Relay/Activity Log] An Activity Log entry is now created when messages are relayed to an email account by a worker or Virtual Attendant.  This notifies other workers that work may be taking place on the ticket from outside of Cerb, and it also serves to keep a better history of the actions of Virtual Attendants.  Previously, there was no record on a ticket that it had been relayed unless a comment was explicitly created to say so.
* [Mail/Activity Log/Preferences] Workers can now enable the display of Activity Log entries on the ticket timeline.  This displays a mix of messages, comments, and activity log data in a single place without having to click into the 'Activity Log' tab.  The option is located on the Settings page that is accessed from the menu displayed when a worker clicks on their name in the top right of the UI.  Consecutive log entries will be combined in a single block, and those that take place with a similar timestamp are grouped together for readability.  This option is also compatible with the 'Read all' option where the timeline is displayed expanded in 'oldest first' order rather than 'newest first'.
6.6-dev checkpoint