Minor change on Liquid Demo app interface

Move the anonymous user identifier into its own button, allowing one to
identify an anonymous user multiple times successively.
Also reuse the last segmented control discrete button to add a new
identified user.

This should allow more freedom on switching users and will allow us to
replicate some bugs caused by edge case uses of the identify user with
anonymous.

Signed-off-by: João Soares <jsoaresgeral@gmail.com>
Merge branch 'minor_improvement_to_liquid_demo' into refactoring
Auto flush running on background

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
Not allow alias if curr. user is anon. & prev. is identified

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>