Address non-modular pages

Crude fix for #8 and #9. For non-modular pages gallery theme must be set in page header and not in template, see corresponding readme section.

Several galleries per page

Pass custom gallery ids (in json or as third argument to unite_gallery function) to create several galleries on one modular page.

Assets handling

Change assets handling to allow twig caching

Configuration bugfix

Fixed gallery div id validation in admin panel

v1.0.0

Initial release