Color field now supports WordPress 3.5 color picker

For WP 3.5+ installs, built color picker (currently Iris) will be used.
Versions below will default to `farbtastic`
Fixed saving issue with autosaved meta boxes

Removed autosave check from `save_post` function, as it caused meta
boxes with `autosave` set to `true` to only save by autosave and not by
a regular update.  A new `autosave` data field is now added to the
`rwmb-meta-box` div, to differentiate between autosave and non autosave
meta boxes
std used for default select option