Merge pull request #22 from oli-obk/feature/html2message
[Build] Reference System.Xml for Engine
[Engine] Updated copyright
[Engine] Coding Style
[Engine] ";" are optional for single CSS style
[Engine] Fixed build on .NET 3.5, WebUtility.HtmlDecode() is .NET >= 4.0
[Engine] Use logger instead of message to output error details
[Engine-Tests] Added basic MessageBuilder.AppendHtmlMessage() tests
[Engine-XMPP] Removed jabber-net2005 and moved to agsXMPP
[Engine-XMPP] Resources and Priorities are now properly supported
[Engine-XMPP] Disable MUC until fully loaded. Open Contactchat on reconnect. Allow custom away messages. Remove outdated comments.
[Engine-XMPP] Engine doesn't crash with old frontends anymore.
[Engine-XMPP] Can now connect through a proxy