chore demo: change the way of including examples

Avoid break line problems by using ng-include rather than hljs include
attribute.
chore demo: refactor mixins hljs
chore demo: enhance installation layout
chore demo: enhance customization layout
chore demo: enhance contribute layout
chore demo: enhance mixins layout
chore demo: add colors documentation
chore demo: enhance buttons layout
fix fab: wrong animation with left direction
chore demo: enhance fab layout