Enhancement : Palette colors creation

- Added cancel button to create palette dialog
- Added escape/unescapeHtml methods to pskl.utils
- Escaping palette name now ...
- Removed outdated comment in app.js regarding appEngine token
- Added a call to destroy() during dialogClose of AbstractDlgCtrl
Moved PaletteService from pskl.service to piskel.service.palette
Enhancement : Palette color creator

- Added import button on create palette dialog
- implemented import from images
- missing limitation on color count when importing !!
- should remove button when editing existing palette