Show username instead of "me" in chat, closes #60

Add a User singleton to get the current user's name

use the own user's name

Initialize the User in the right place

Use a string instead of a Contact in User.vala

Set the right users name in outgoing messages

Show username instead of "me" in chat, closes #60
Merge branch 'dontshowme' of https://github.com/blackwolf12333/Venom into dontshowme