MyCyma

[fix] corrected sort on artworks index

[cosmetic] repeat pagination and new action controls in artworks administration page (closes #88)

[evol] artworks context menu: finished mechanism + checked for empty selection + implemented associate_with_tag action

[evol] preliminary artworks context menu (reverted license to GPL2+, to be compatible with Proto.Menu and possibly other plugins)

[evol] added tags and fixes a few typos

[evol] added more links from artwork steps to the artwork

[fix] ensure the default display size for a thumbnail (currently the full image) does not crash (closes #77)

[fix] handle image/thumbnail errors better in helpers

[fix] ensure ArtworkStep has a non-nil/NULL 'position' (not set in ArtworkStepThumbnail for example)

[evol] added helper methods for ArtworkStep<Image|Thumbnail>