Added StaticContent helpers

A tiny DSL for adding static files and directories in the Bootstrapper
Update StaticContentHelper.cs
Update StaticDirectoryContent.cs
Update StaticFileContent.cs
Update StaticContentHelper.cs

Late night.. juck..
Update StaticDirectoryContent.cs

Added allowedExtensions
Added param allowedExtensions Description
Renamed 'Static' to 'MapStaticContent'
Merge pull request #1064 from davepermen/tinystaticdsl

Added StaticContent helpers