Redirect with username and tracking ids

[jnordberg]

Condenser supports autofill in the login form, we should use that when redirecting:

https://steemit.com/login.html#account=billbonds

And we also need the ability to pass along identifiers that are carried along trough the process and sent to the DEFAULT_REDIRECT_URI

---

Spec:

1. Values passed via query strings to first step are carried through the signup process
2. Redirect uri is resolved via templating
   1. Variables in template look like: {{variable_name}}
   2. username is special and is populated by newly created username and not overridable by first step query strings

Example: With DEFAULT_REDIRECT_URI set to https://example.com/{{username}}?foo={{bar}} and an initial entry point to step1 with ?bar=man and new username baz the redirect url should resolve to: https://example.com/baz?foo=man

Tests:

• Template: DEFAULT_REDIRECT_URI="http://localhost:1234/{{username}}/foo?u={{username}}&id={{id}}
  • New username: monika
  • Step 1 query string: ?id=1234
  • Result: http://localhost:1234/monika/foo?u=monika&id=1234
• Template: DEFAULT_REDIRECT_URI="https://example.com
  • New username: monika
  • Step 1 query string: ?id=1234
  • Result: https://example.com
• Template: DEFAULT_REDIRECT_URI="https://example.com#{{username}}
  • New username: monika
  • Step 1 query string: ?username=hax
  • Result: https://example.com#monika

[gregory-latinier]

Ok I'll modify the code to match the specs