Add some new sign-in/up tracks

[hypest]

Addresses #4903

Adds tracks for:

• Default/Main Sign in screen displayed
• Create account initiated
• Email already used (error) when creating a new account/user
• Username already exists (error) when creating a new account/user
• Failed to create a new account

[daniloercoli]

What's about tracking the network error details in properties?
Something like the following code (that I didn't test)

Map<String, Object> properties = new HashMap<>();
properties.put("network_exception_class", error != null ? error.getClass().getCanonicalName() : "null");
properties.put("network_exception_message", error != null ?  error.getMessage() : "null");
if (error.networkResponse != null) {
     NetworkResponse networkResponse = error.networkResponse;
     if (networkResponse.data != null) {
             properties.put("network_exception_data",  new String(networkResponse.data)););
      }
}

[hypest]

Hey @daniloercoli , good point. I actually looked into adding error info to that track prior to opening the PR but it seems that the useful error message can be deeper in the response's body. Most of onErrorResponse()'s code is about extracting the message after all. It seemed too complex for the purposes of this PR and decided to leave it out for a future PR if we see the need.

That said, let me know if you think this is a blocker and we should address it within this PR. Thanks!

[daniloercoli]