[text chat integration] blocked by chrono-chat bugs

- current chorno-chat based on ChronoSync2013 from NDN-CPP does not
provide reliable message delivery; chat integration will be resumed as
soon as fixes will be ready
fixed blinking to black in rendering window
[bugfix] fixed random crash on closing app with active conversation
added outgoing bitrate estimation to statistics window
[feature] added drag&drop functionality for user list

- user can be added to the current conversation by dragging a user view
from the user list onto the conversation view
[feature] added drop ability to conversation view
[feature] fetch missing streams

- upon adding user to the conversation, check which streams are
currently fetched and fetch only missing ones
[bugfix] fixed random crash when switching b/w streams

- sometimes when switching between several video streams, app was
crashing; fixed it - OpenGL-related multithreaded problem (accessing
OpenGL context when it was not ready yet)
'issues/stability-bugfixes' -> 'dev'
[in progress] conference discovery

- added conference discovery library controller
- added conference list UI
- added Conference entity to data model
- updated current version of data model
updated data model, conference UI

- added organizer to the conference
- implemented UI for viewing conferences
implemented interface for adding and editing conferences
conference management logic

- implemented: conference discovery, conference editing, publishing
[bugfix] exception on MacOS 10.10.

- fixed exception on MacOS 10.10 upon starting conversation
implemented in-conference logic

- adding participants of a meeting once they are publishing
- removing participants from the meeting if they stop publishing
- code refactoring
- minor bugfixes
NdnCon v0.2.0
'dev'->'master'