Added acts-as-taggable-on gem for tagging questions and articles. Added Tag controller, which shows all tags and all questions and articles tagged with specified tag.
Merge branch 'adding-tags'
Updated styling for articles, reactions and comments.
Added tags to projects.
Merge remote-tracking branch 'origin/master'

Conflicts:
	app/views/projects/show.html.slim
Added missing controller_helper for testing.