Update Skin 18 and icons

[HenriqueLimas]

• [x] Update to Skin 18
• [x] Update icons

Lightbox Dialog @HenriqueLimas

• [x] add support for size "fullscreen" and "large" #353

Icons class update: assigned to: @HenriqueLimas

• [x] change class to "icon--{size}" #352
• [x] For filled, remove the size from the name and add icon--{size} #352

Textbox structure @HenriqueLimas

• [x] remove textbox--icon-end class #354
• [x] Use textbox--(disabled, invalid, readonly, large, fluid) classes instead of textbox__control #354
• [x] Add prefixText and postfixText support, add aria-describedby referencing them #354