Test static files

[rspilker]

I've created some tests on the staticFiles feature:

• Get text file from main directory, with the right mimetype
• Get html file from a subdirectory, with the right mimetype
• Get a file with an unregistered file extension with mimetype text/plain
• Get a 404 is the file is not found
• Get a 404 is the users tries a path traversal attack (/../).