Update report's scrollview with better stability. closes #373

Improvements:
- A delay was added (ReportView.cs) before try a call to remote server. In case of fast scrolling, the delay will be canceled.
- The IsLoading state was updated. (SummaryReportsView.cs)
- A better method for calculate current report view. (InfiniteScrollView.cs) 

Fixes #373
Why this change? From first look doesn't make much sense to introduce more code instead of compiler generated private getter.