added index and show actions in topics controller #307
added age method in child and registereduser model #307
added associations in child,activity,topic,activity_account models #307
added method available in activity model #307
added background images for animation #307
added index,show views for topics #307
added routes #307
added documentaion and code conventions #307
added code conventions #307
added missing documentation #307
merged with development #307
Merge pull request #381 from yousraHazem/c4_s22_As_a_child_I_should_belong_to_all_of_topics

22 - As a child I should belong to all of the playground's topics