Added classes m*0 and p*0

Removed classes nomargin/nopadding (too limited).

Added classes :
- .mt0 (margin-top: 0;)
- .mr0 (margin-right: 0;)
- .mb0 (margin-bottom: 0;)
- .ml0 (margin-left: 0;)
- .m0  (margin: 0;)  

Same for padding.