Popup should initialize to default interface, then change if error

[rjpeterson]

Current popup function is to initialize to "loading..." and then load interface after response is received from injected content script.

This works OK but results in significant delay when content script injects slowly like on Edge browser.

Instead, we should load basic interface first and allow user to input values immediately even if content script is not injected yet.
If script injects successfully, send content object. If not, display error.