cleaning current_server_helper_method
using of host_with_port
Adds admin/essences helper to Admin::ContentsController.
Merge pull request #358 from skeller1/current_server_cleaning

cleaning current_server_helper_method
Only replace essence picture thumbnail if picture is assigned.

Closes #355
Ensure that only true enables the image float selector. Closes #357
If essence picture has caption, the css class should be on the wrapper element. Closes #356
Fixes redirection after signing out.