Keep state for LN > LQ swaps

[bordalix]

This PR:

• splits receiving in lightning into 2 differet routes:
  • insert amount
  • show invoice
• stores on local storage amount inserted and swap data
• if the user already inserted an amount, when coming back will see that page with previous amount
• if user closes the popup before ending the claiming (ie receiving LN), he can now re-open it and the app will remember and finalize the claim tx

closes #510

@tiero please review