Merge: Renaming of coordinate space attributes [ following the Hackathon ]

As agreed at the hackathon with @jbpoline, @gllmflndn and @nicholst (cf. #68). This is a proposal to rename some of the `coordinateSpace` attributes as follows:

 - `coordinateSystem` -> `worldCoordianteSystem`
 - `dimensions` -> `dimensionsInVoxels`
 - `coordinate1InUnits` -> `coordinate1`
 - `coordinate1` (in FSL ) -> fsl:coordinate1InVoxels (in the definition specify if origin is 0 or 1). 0 is nifty spec.