Show error when target is not visible in the Window section

[jnation3406]

This is stuff Blanco requested, but I think it makes sense for everyone. Two changes:

• Renaming the label for a RequestGroup name to Request Name from just Name - I guess it was confusing since some people thought it meant a persons name should go there.
• When a target is entered and not visible, the error shows up at the Request level, and the Window section just doesn't show an Airmass Plot. This change is so that the error from the /airmass/ endpoint is incorporated into the Window section error, so if a target is not visible, the window visibility error should show up in the Window section and at the top of the Request.