sort conversation by time of entry creation, not just id
improve presentation users in the dialogues list

For dialogues between users where neither is the current user,
the user without mod/dialogue:manage permission is presented
as the primary in the dialogues list. Also, when viewing a dialogue
between two users neither of whom is the current user, the 'Dialogue
between X and Y' form of message is presented.
typo in 'dialoguebetween' lang/en string
Fixed settings file, had weird new lan_string() calls
Merge pull request #26 from jonof/usq-improvements

Improvements to dialogues list presentation
Fixed Strict standards error that was being showing on recent activity block
Updating version file 2.4 release candidate
First drop of the completely rewritten dialogue module
Document dialogue conversation/reply message state constants
Updated action buttons CSS classes and automplete placeholder
Added new trashed state and removed redundant cache method get_user_brief_details
Created a separate render method for reply class, reverted lang_string calls to get string and some documentation.
Tidy up of code in conversation page
Changed get_string for trashing a conversation
Tidy up of code in reply page
Added redirect to drafts page for save and trash submission actions
Fixed check on conversation page to see if still open and can display reply form
Added a session cache to remember application state for user experience
Added function to cache params for course module instance, used in display controls to remember state for user experience
Various strings added