[WIP] 10173: save criteria and duplicates

[eliserichards]

For mozilla-mobile#10173

• make call to AC to get dupes list
  • need some review on the async coroutines calls
• pass list to fragment (from the controller?)
• always check username edits against dupe list
• have a global "save enabled" state
  • set this on any text change?
  • ensure that username & password aren't overriding saveEnabled when they shouldn't be (e.g., username is invalid and saveEnabled = false, but you click on pwd and edit to a valid state. saveEnabled shouldn't be set to true on password edit)
• Tests!
• keyboard clicks to show/hide