adding support for other channel types with auto-scale

[choldgraf]

This is a quick extension of #3198. I realized that the function would only pull eeg or meg channels when computing the auto-scaling, but we probably want auto-scaling to work for any channel types. This should add support for the remaining channel types.

[coveralls]

Coverage increased (+0.004%) to 90.857% when pulling a18814e on choldgraf:add_ch_types_auto_scale into 5a71c71 on mne-tools:master.

[choldgraf]

oops, discovered the channel_indices_by_type after I first pushed this. I think that's probably what we should be using. Cuts back on extra imports and I think simplifies the code a bit. That look OK?

[coveralls]

Coverage increased (+0.001%) to 90.855% when pulling 7ae9baa on choldgraf:add_ch_types_auto_scale into 5a71c71 on mne-tools:master.

[coveralls]

Coverage increased (+0.001%) to 90.855% when pulling 7ae9baa on choldgraf:add_ch_types_auto_scale into 5a71c71 on mne-tools:master.

[larsoner]

Thanks @choldgraf