refactor directives

- demo: fix highlightjs and change file names
- getting started: enhance documentation
- mixins: add documentation
- colors: add background colors, text colors, and colors settings
- buttons: replace black buttons by blue buttons
- fab: fix animation
- icons: add simple icons and enhance documentation
- toolbars: add search filter in documentation
- dropdowns: refactor directive
- tabs: refactor directive
- text-fields: refactor directive
- search filter: refactor style
- selects: include search filter and fix style