Display current project at the top in helm-projectile

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.
Allow helm-projectile to open multiple selected files

Now users can select files with "C-SPC" or select all with "M-a", then
execute the first action in the action menu or press RET, all the marked
files will be opened.
Merge pull request #437 from tuhdo/master

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