Rename Margin/Padding Classes

[JakeDawkins]

The current classes for margin and padding (hard/soft, push/flush) are a bit too abstract, and sometimes difficult to remember which class maps to what effect.

A new naming of the modifiers to more closely match the CSS representation would be helpful

The new classes would be as follows:

Margin
mar-zero-top
mar-half-sides
mar-quarter-left
etc...

Padding
pad-zero-top
pad-half-sides
pad-quarter-left
etc...