Show federation record memo in send payment view

[ebma]

• Lookup federation record on destination input change
• If a federated address enforces a memo disable the memo input field, fill the memo input with the required memo text and show Memo (Text) or Memo (Id) depending on type in the label
• Show "Stellar Address does not exist" error message when destination matches scheme of a federated address but no record was found

Closes #714.

[andywer]

Memo to myself: Still need to test this.