Convert CSS padding and margin properties

[epsitec]

Both padding and margin properties can be either written using a shorthand property (padding) or longhand properties (padding-bottom, padding-left, padding-right, padding-top).

Note: using short hand properties does not produce expected results in React or Radium
when several styles get merged together while mixing longhand and shorthand properties.
Sticking to longhand properties ensures that there are no unexpected behaviors.

Add function getLonghandProperties to Electrum, taking a style object and replacing all shorthand properties with longhand properties:

• getLonghandProperties (style) → style

[epsitec]

There are other properties (a complete list would be welcome) which map to multiple properties (for instance some flex related properties). We should also address these.