Guess image format on image::Handle::Path load

[SoulSharer]

Currently there is an inconsistency with image loading. If Image is loaded from bytes image::Handle::from_bytes(bytes) - format is guessed by content, but with image::Handle::from_path(path) it is guessed by file extension, which might not be present.

In the comments it is said to examine the data in the file.

/// Creates an image [`Handle`] pointing to the image of the given path.
///
/// Makes an educated guess about the image format by examining the data in the file.
pub fn from_path<T: Into<PathBuf>>(path: T) -> Handle {
    let path = path.into();

    Self::Path(Id::path(&path), path)
}

So this PR fixes this inconsistency to guess the format by contents instead.