fix(ngdocs): make jsFiddle and Plunkr links work with external AngularJS modules
chore(ngdocs): fixed jsFiddle/Plunkr examples to include ngAnimate and use a default App the module is not set
fix(ngClass): ensure ngClass doesn't fire addClass or removeClass with an empty string

If ngClass fires off an add- or removeClass whilst the opposite animation is going on then
the animation will be skipped. The default behavior of ngClass was executing remoteClass
with an empty string while addClass had just fired. This commit fixes that bug.
chore(ngdocs): all animation-supported directives working with docs examples and jsFiddle/Plunkr pages