Metadata files use consistant key names

Using any of 'title', 'comment', 'tags', the application will
set 'date', 'filename', 'url_html', 'url_img' on its own
HTML pages per image

Image pages display a larger copy of the file plus metadata and a link to
the original file.

Changed image routes and image listing offset format.

Specify images-per-listing-page in config.
Typofix