5.6.0

Features

• add gallery.service to call modal-gallery methods without plain gallery.
  In this way you are able to open modal gallery to an image by its index, without clicking on a thumb, but via Component's code.
  This feature closes these two feature requests #127 (@pieterdegraeuwe) and #131 (@tobi-or-not-tobi)

Testing

• add unit testing for both component and service

CI

• improve CI configs