.NET RegEx to remove whitespace in allowedReferers

in the .NET proxy.ashx, added a RegularExpression to remove whitespace
characters from the allowedReferers.

This lets us put in spaces, line breaks, tabs, etc. to keep the
proxy.config looking well formatted and easy to read, but still lets the
proxy.ashx split the string at commas.
Merge pull request #159 from robkspeer/rob_stripWhitespaceInAllowedReferers

Remove whitespace in allowedReferers (DotNet)