Add configurable color for Input autocomplete

[issadarkthing]

It would be convenient if we can configure the color of the autocomplete for InputField instead of using global Styles.

[gpanders]

I'd like to add my support for this feature. The inability to style the autocomplete list separately from the rest of the primitives is fairly limiting, particularly when trying to support both light and dark terminal backgrounds.

[gpanders]

@issadarkthing I actually don't think this will work. In the Autocomplete function, the list is destroyed and re-created repeatedly:

tview/inputfield.go

Lines 232 to 248 in d4fb034

	entries := i.autocomplete(i.text)
	if len(entries) == 0 {
	// No entries, no list.
	i.autocompleteList = nil
	return i
	}
	// Make a list if we have none.
	if i.autocompleteList == nil {
	i.autocompleteList = NewList()
	i.autocompleteList.ShowSecondaryText(false).
	SetMainTextColor(Styles.PrimitiveBackgroundColor).
	SetSelectedTextColor(Styles.PrimitiveBackgroundColor).
	SetSelectedBackgroundColor(Styles.PrimaryTextColor).
	SetHighlightFullLine(true).
	SetBackgroundColor(Styles.MoreContrastBackgroundColor)
	}

Instead, you either need to 1) add a new hook that can be called for the autocomplete list to be configured after it's created or 2) add new properties to InputField (autocompleteTextColor, autocompleteBackgroundColor, etc.) and use those to set the autocomplete list styles in lines 243-247.

I have a PR ready to go that does the latter: gpanders@c5d98ee