URBNG-131 - [WP] create service/listener for handling changes in game that user has joined   

Mock-up of GameEventAggregator wasn't necessary because of architecture (publisher - subscriber).

Also:
- removed unnecessary *.csproj.user files
- removed GameChanged event from WebService, interface and tests
- GameWebService and GameEventAggregator instance moved to BaseViewModel
- TaskMock.cs moved to BOMock folder