[Xamarin] Setup basic component using PCL libs.

Added a working component with three PCL libs, and two samples.
The libs consist of the SignalR client and two dependencies.
The icons, markdown files, and metadata need to be polished
and it will be ready for submission.
[Xamarin] Updated component summary.
Made building Xamarin component part of the build and added additional files
Added debug symbols for Samples
Removed Samples from the Xamarin package
Removed client DLLs from the Xamarin package
Modified build and added files within the Xamarin lib folder to gitignore
Added sample for Xamarin component
Made changes as per code review feedback