Project topics: Add management in admin area

app/assets/javascripts/pages/admin/topics/edit/index.js

app/assets/javascripts/pages/admin/topics/new/index.js

app/controllers/admin/topics/avatars_controller.rb

app/controllers/admin/topics_controller.rb

app/controllers/uploads_controller.rb

app/finders/projects/topics_finder.rb

app/helpers/avatars_helper.rb

app/models/concerns/avatarable.rb

app/models/projects/project_topic.rb

app/models/projects/topic.rb

app/views/admin/topics/_form.html.haml

app/views/admin/topics/_topic.html.haml

app/views/admin/topics/edit.html.haml

app/views/admin/topics/index.html.haml

app/views/admin/topics/new.html.haml

app/views/layouts/nav/sidebar/_admin.html.haml

app/views/shared/empty_states/_topics.html.haml

app/views/shared/notes/_hints.html.haml

app/views/shared/topics/_search_form.html.haml

config/routes/admin.rb