Refresh chat list when opening

@sinan, can you review this fix? it's related to https://www.pivotaltracker.com/story/show/84458586 and fixes several bugs found in collaboration chat:
- custom scroll bar doesn't work when you open chat and it already has existent message
- long messages are not truncated and 'show more' links are not visible at the same case as before
pane's refresh() method can be found in changes of https://github.com/koding/koding/pull/2302