check forum read permissions when user replies to topic/post

Fixes #445
Fixes #446
Mention rails4 support in the README
mention necessary gemfile line for friendly_id for Rails 4
Specify cancan dependency also in readme
Switch to using Bootstrap CSS

Conflicts:
	app/views/forem/admin/categories/index.html.erb
	app/views/forem/admin/forums/index.html.erb
	app/views/forem/posts/_post.html.erb
	app/views/forem/topics/show.html.erb
Add btn-primary classes to categories form button
Fix category edit title
Change theme image
Correct README line for theme
Merge branch 'master' into rails4

Conflicts:
	app/views/forem/admin/forums/index.html.erb
	app/views/forem/posts/_post.html.erb