Bring back `.btn-mini`

Created by: pvdb82

Hi,

ist have following hints:

• The glyphicons icons are not vertical centered in the buttons, they are on the bottom (I bought the glyphicons)
• The mini button set is missing (please add them again)
• Please add again the old btn button style. The new default button is too dark. The default button on bootstrap 2 looks much better
• The new button do not really looks like button