Adding Comments, Image description and Modified time to properties dialog

[sjoblomj]

Extends the fields in the Properties dialog.

Will now show

• Date and time when the file was modified
• JPEG comment
• Exif.Image.ImageDescription
• Exif.Photo.UserComment

Inspired by https://github.com/hellosiyan/Viewnior/pull/14

Closes #51

[hellosiyan]

@sjoblomj Thanks for your work, looks great! There are a few sections which I am not sure I understand entirely, I will go ahead and comment.