File: added extension whitelist check for files to prevent dangerous files from being uploaded.

Whitelist is checked on file creations.

(cherry picked from commit 4a566210678eb80dca3f7a12262791f2d671bbb7)

Conflicts:
	ED47.BusinessAccessLayer.EF/LocalFileRepository.cs
	ED47.BusinessAccessLayer/File/FileRepository.cs
	ED47.BusinessAccessLayer/FileRepository.cs
	ED47.BusinessAccessLayer/IFileRepository.cs