Second iteration of user story editing.
Creating AddStoryToSprintForm (prototype)

TODO: add logic
Merged urejanje_inbrisanje_uporabniskih_zgodb3 to master
Merge branch 'add_story_to_sprint'

Merged add_story_to_sprint to master
Completed story AddStoryToSprint. Need to be tested.
Editing user story from product backlog
merging master
Editing user story from product backlog
Editing user story from product backlog
Editing user story from product backlog