Generalize swizzles to work with any storage type

[arturoc]

Right now the swizzles in nalgebra-glm only apply to vectors (with owned storage) if they were generalized to 1 column matrices of other storage types it would allow to do things like:

let mat = look_at(...);
let z_axis = mat.column(2).xyz();

Perhaps the swizzles could be moved to nalgebra so they can also be implemented for other types like points?

[arturoc]

Sorry I assumed wrongly that swizzles were implemented for owned storage only and in glm when they are already implemented for any type of storage