[Engine-XMPP] created invite command

note, this is only delegated invite, direct invite is not supported by agsxmpp
[Engine-XMPP] added "addgroup" command to add a contact to a roster group
[Engine-XMPP] Show message when invited to a muc

Note: the generated join-hyperlink is not supported by smuxi yet
[Engine-XMPP] fix adding contacts to roster for some servers

some servers don't follow the standard properly, they only properly support subscribing to/from contacts that are in the roster
[Frontend-GNOME-XMPP] specialize PersonChatView for xmpp
[Frontend-GNOME] remove extra scheme check for urls
[Frontend-GNOME-XMPP] invite menu in private chat context menu
[Frontend-GNOME(-XMPP)] WIP
[Engine-XMPP] refactored CommandMessageQuery (/query or /msg)
[Engine-XMPP] simplified XmppPersonModel generation
[Engine-XMPP] notify user of unknown illogical presence changes
[Engine-XMPP] check engine version before calling new ExecuteUri function
[Engine-XMPP] show human readable message on two common disconnect reasons
[Frontend-GNOME-XMPP] add people from muc to roster through nicklist context menu
[Engine-XMPP] get real jid of muc contacts
[Engine-XMPP] refactor whois command
[Engine-XMPP] Simplified presence processing

presence notification generation is now separate from contact list updates