Display current project at the top in helm-projectile and allow open multiple files

Since the displayed projects in helm-projectile is not used merely for
jumping but for other actions. Without the current project displayed,
it's difficult to perform action like helm-do-grep from project root.

Also, Helm is capable of opening multiple files, so should Projectile.
Guess you can use the list of all known projects as the code looks a bit confusing as is.