CDB-1758 Add basic image metadata extractor

image = CartoDB::ImageMetadata.new(file_path)
image.width
image.height
CDB-1758 Test svg output on CartoDB::ImageMetadata WITH LOTS OF LOVE
Add .ruby-gemset to gitignore
Update debugger gem
CDB-1758 Add file dimensions validation on Asset model
CDB-1758 Fix assets api spec, fix error removing assets from s3
upload assets working in development environment
resolution error added to asset manager
CDB-1758 Fix asset spec
CDB-1758 Fix assets api specs