Add network and networkwidgets modules
Improve TNetworkClient
Change; feature

* Implement new TNetworkClient methods
* Change network widgets (pass TNetworkClient instead of pointers to functions)
Change; fix

* Move TGroupWidget to networkwidgets module
* Fix client interaction in networkwidgets classes
Implement proxy models
Change; fix

* Check client state in network widgets
* Check client access level
Change

* Make *Model classes methods virtual
* Add TUserModel methods for storing avatar separately
* Use TUserModel in TUserInfoWidget and set user by id, not full info
Change; fix; feature

* Improve *Model classes
* Fix TUserInfoWidget
* Add TUserWidget class
Improve TUserInfoWidget (EditSelf mode)
Update version
TeXSample v2.0.0-beta3