add multiple option for select

[sbeam]

when option "multiple" is true, will process original value as array (joined on comma for now for display), and then pass array of selected options directly back to controller. Always adds a button because the change event is often fired spuriously when interacting with a multiselect.

(there seems to be desire for this feature (eg, #285) and it's working in production for me. Feedback welcome - PS this gem is great :+1: )

[sbeam]

getting an unrelated failure on "should be able to use bip_bool to change a boolean value using an image" locally on master, and now on CI as well. Not sure what is going on with that, will look into if I get a sec

[EmmaB]

This is great, although I'm getting Uncaught TypeError: Cannot read property 'indexOf' of undefined when there is no value.

[sbeam]

@EmmaB good catch - I made a commit to deal with that, does it work better?

[EmmaB]

@sbeam Sorry for the slow reply -- yes, that works perfectly.