feat(usernames): mix dash warning

[Syn-McJ]

Issue being fixed or feature implemented

We want to warn the user that their balance should be mixed before creating a username.

What was done?

• Converted a bunch of username flow screens from Obj-C to Swift
• Added a "Mix your dash" bottom sheet dialog
• Show the dialog on the Home screen, Main Menu, and Contacts screen

How Has This Been Tested?

QA

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[pankcuf]

LGTM