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
Remove jquery.autocomplete in favour of select2

Conflicts:
	forem.gemspec
Improve admin navigation
Fix tests broken due to recent Bootstrap changes
No more Ruby 1.8 support for you.
Fix MySQL build failure caused by posts created too closely together (forum_spec)
remove dependency to bootstrap-sass
add missing a closing div
Merge pull request #452 from jugyo/add_missing_closing_div

add a missing closing div
remove needless "`" from view
Merge pull request #453 from jugyo/patch-1

remove needless "`" from view
Merge pull request #450 from jugyo/remove_dependency_to_bootstrap_sass

bootstrap-sass isn't needed by default