Fix some actions and reformat code to look better

These Helm actions are fixed:

- Improve helm-projectile-switch-to-shell: make it also work with
  helm-projectile-find-file. Reuse helm-ff-switch-to-eshell.

- Fix "Helm Etags Select" action: now from helm-projectile-find-file, the action
  helm-etags-select can be invoked to list all available tags. User
  must generate a TAGS database and load into Emacs with visit-tag-table
  first. While in helm-etags session, pressing "C-c p f" switches back
  to helm-projectile-find-files.

- Fix "Eshell command on file(s)" action: now properly retrieve files to
  run commands on.

Signed-off-by: Tu Do <tu.h.do@dektech.com.au>