Merge pull request #14 from Pessimoi/master

Artist page and stuff
Add AsyncLock, AsyncSemaphore and LazyAsync (LazyAsync not tested yet)
Make DataLoader static
Add new "Refreshable<T>" API
Revert startup page to main page again
Artist list clicking
Remove unnecessary library
Artist play on youtube
Added WP Toolkit
GetPageUris added
Add LoadingIndicatorHelper and use it in MainPage
Add cancellation to LazyAsync (not tested)
Quick and ugly image loading synchronization
Set Controls.AsyncImage.Factory
Artist list proper loading from the net
Removed MainViewModel and corrected starting page
Add Events API and update Artist model
Add locations to api
Update design time jsons
Remove unused code