Improved image format detection

Detection is based on the first two bytes of the original file.
If it corresponds to the JPEG "first bytes" signature, it assumes that it's a JPEG.
Merge pull request #4 from mguillermin/guess-image-format

Improved image format detection
Update Image.scala

fixed assert
added name attribute to file input

added name attribute to file input so the server detects the uploaded files
Merge pull request #6 from ggmoriyon/patch-1

assert was missing a parenthesis, causing Boxed Error
Merge pull request #7 from ggmoriyon/patch-2

added name attribute to file input