require pry and pry-nav gems in spec_helper

This helps debuggig, so you don't have to manually require these gems in
your tests
Use save! to raise errors if validations fail, when saving record
Write test for Releaf::Node#content_class
Optimize query
use foo.present? instead of !foo.blank?
Optimize query and improve readability of Releaf::Node#available?
Fix Releaf::Node.updated_at test

By simply updating Releaf::Node.updated_at to return current time, it
was possible to trick this test to pass, while functionality would be
broken
Don't abuse subject, it has special meaning in rspec
Node name is not important for Releaf::Node#available? test
Use predicate matchers in Reelaf::Node#available? tests
Add missing Releaf::Node#destroy test case
Remove unneeded line

Slug was set to nil in code below
Remove duplicate, inferior test
use #class#name instead #to_s to get class name of instance
Serialize Releaf::Role#permissions as array
Validate presence of role, not role_id in Releaf::Admin
Add test for Releaf::Role#admins associations
Remove extra newline to prevent documentatio errors
use foo.present? instead of !foo.blank?