Remove "Runtime" from all namespace reference, sort namespaces as per .net convention and enforce the same.

[Zruty0]

Remove "Runtime" from all namespace reference, sort namespaces as per .net convention listed below and enforce the same.

SA1210: Using directives must be ordered alphabetically by namespace.
SA1208: System using directives must be placed before other using directives.

[codemzs]

@TomFinley As part of this change we will be sorting and removing unused namespaces. For sorting is it ok if we list System.* namespaces first in sorted order followed by remaining namespaces also in sorted order.

[codemzs]

SA1210: Using directives must be ordered alphabetically by namespace.
SA1208: System using directives must be placed before other using directives.

[justinormont]

I created a sub-issue (#1964) to update the example code.

[codemzs]

Thanks @justinormont !