Added preview for answers

I have added a preview feature for answers similar to questions. I
have also filtered out links in the navigation bar when no one
is logged in. Further work needs to be done to do role specific
filtering.
Modified the form validation

I have modified the forms to be validated by angularjs to not
only display error messages but also to stop the request from
going to the server if a requirement is not met (eg. missing field).

I have also fixed judgepage to be capable of rendering math
equations.

New form css classes have been created, default and alternate. Default
is currently being used for forms like create user. Alternate is being
used for forms like create course that has very few fields and are
inlined with other texts.