Improved the import support

Hi,

I have made some minor changes to get better @import support for this adapter. Before you couldn't have less files in different folders if they had @import statement since the ImportedFilePathResolver only where set the for the first file. 

You can find an example (~/bundles/files-from-different-folders-with-imports) on this issue in the BundleConfig file in the MvcApplication.

I also changed so when working locally the EnableOptimization flag is followed meaning minification will only occur when that flag is set or when you run in a none debug mode.

I hope you could merge these fixes in and release a new nuget package.

Thanks in advance!