RF: deprecate image rollaxis and do minor refactor
RF: deprecate image rollaxis and do minor refactor

Deprecate image rollaxis in favor of brank-spanking-new function.

arokem/nipy,nipy/nireg,alexis-roche/nipy,arokem/nipy,alexis-roche/niseg,arokem/nipy,arokem/nipy,alexis-roche/nipy,bthirion/nipy,alexis-roche/register,alexis-roche/nipy,bthirion/nipy,bthirion/nipy,alexis-roche/nireg,nipy/nireg,alexis-roche/niseg,bthirion/nipy,nipy/nipy-labs,alexis-roche/nipy,nipy/nipy-labs,alexis-roche/register,alexis-roche/nireg,alexis-roche/register