Add Interactive Mode

[jradavenport]

Need to add interactive features for:

• ap_trace
• HeNeAr_fit
• others?

[jradavenport]

Primitive version of interac=True for HeNeAr_fit done. Currently emulates the IRAF task IDENTIFY. Workflow is:

• click on feature
• type in wavelength

Thinking about alternative workflow:

• auto-identify first
• reject bad peaks?

Will be easier to do the interac=True mode for ap_trace now