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
Remove jquery.autocomplete in favour of select2

Conflicts:
	forem.gemspec
remove needless "`" from view
add locale data for forem.admin.forums.index.no_category
fix some links to forums page for consistency
remove defunct sites from list
Mention about Vietnamese translation in README

[ci skip]
Correct check for a tag in formatting_spec
Remove simple_format from formatting_helper

This was causing more trouble than it's worth, and besides the formatters for Textile + Markdown already add in the paragraphs, so there's no point using simple_format if the formatters are supposed to do it anyway
Failing spec for redirecting posts#show to topics#show
Redirect posts#show to topics#show