[fix] ensure ArtworkStep has a non-nil/NULL 'position' (not set in ArtworkStepThumbnail for example)
[evol] added helper methods for ArtworkStep<Image|Thumbnail>
[fix] tries to regen missing thumbnail
[cosmetic] added position number to artwork_step_images, only visible in the admin pages, to be able to change order for steps made the same day (closes #16)
[cosmetic] artwork_sizes height and width are now integers in the DB, and displayed with the corresponding unit (closes #14)
[evol] ArtworkStepImage: added helper method to get a thumbnail by size
[fix] work around steps order when done at the same date (considering people would add them in chronological order) using image id
[fix] wrong method call
[evol] an artwork can have multiple materials
[fix] renamed 'technique' into more appropriate name 'artwork_support', and update schema and translations (Closes #4)
[fix] improve password validation #2
[fix] improve password validation
[fix/evol] forgot new files in the previous commits and check admin status to access user management
Initial version