Updating to latest version of Glyphicons Halflings set (v.1.5) along with some icon enhancements like:

- Updated the Gylphicons Halflings set to version 1.5 (30 new icons)
- Optimized the sprite PNG files for minimum filesize without any quality loss
- Made some fixes for horizontal alignment at the LESS/CSS level (tags, bold, arrow-up, minus, chevron-down)
- Made some fixes for vertical alignment at the LESS/CSS level (chevron-down, resize-vertical, resize-horizontal)
- Renamed the old "calendar" class as "list-alt" class (because now we've a real calendar icon)
- Changed the "background-position" of the icon class to "14px 14px", so that a wrong class name will not be showing the glass icon and instead will show a blank icon (which is useful for just positioning the text after the icons in some cases)
- Added new icons (classes) to the base-css Docs (to both HTML file and Mustache template)
- Changed one of the button examples to danger style and used a white icon
- Renamed the sprite image files to save a few bytes here and there (from glyphicons-halflings-sprite.png to lyphicons-halflings.png and from glyphicons-halflings-sprite-white.png to glyphicons-halflings-white.png)