Keyword replacement to show MSN display name

[andrewallcorn@gmail.com]

A keyword, for example %displayName%, which was replaced with the user's MSN display name would be useful for message styles. It could default to email address or alias if the service was something other than MSN.

[evands]

How would this differ from %sender%?

[Hawkman <hawkman@…>]

%sender% changes according to the user's preferences. Whilst desirable in some circumstances, it makes it impossible to show full information for a contact - for instance, the following might be used in a tooltip:

Alias (MSN display name) - email

Using the current two available keywords, it's not possible to differentiate between the Alias and the Display Name - either could show up, or even the contact's email address, depending on the user's preferences.

This should possibly be a more general request for specific control over which variation of a contact's name shows up at any given time, primarily in order to be able to give multiple pieces of information.

[evands]

(In [14624]) Added %destinationDisplayName% for header/footer and %senderDisplayName% for messages to the webkit style substitutions. These substitute to the serverside display name (e.g. MSN display name) if possible and otherwise fall back on the normal display name.

Fixes #239