Show actionable empty-text on sidebar

[chalkos]

Show the "Please select items using the checkboxes" text on the sidebar when no actions are available, to avoid having an empty sidebar in that case.

This can be further improved by showing different messages (like "You do not have the required permissions to...") or even completely hiding the sidebar depending on why the actions are not showing.

[chalkos]

Do not close this. The above commit (https://github.com/keeps/roda/commit/9df76fcc5f33ce248769be51df636b592bc24596) solves this but it is not the ideal solution. I will get back to this when finding a (better) solution to this issue becomes a priority.