Extract `addStandalone` from `saveToFile`
Extract `addStandalone` from `saveToFile`

This removes quite a lot of checks in favor of single
`switch-case`. Everything related to `standalone` is thus
contained within this single function.

miscco/matlab2tikz,matlab2tikz/matlab2tikz,egeerardyn/matlab2tikz,RPeschke/matlab2tikz,egeerardyn/matlab2tikz,PeterPablo/matlab2tikz,matlab2tikz/matlab2tikz,nidrosianDeath/matlab2tikz,LJeub/matlab2tikz