Custom Actions like Parcellite

[majal]

Is your feature request related to a problem? Please describe.
Parcellite's custom Actions give power to Linux geeks. I use it a lot to perform modifications in my clipboard, from simple "give me today's date" to complex transforms using scripts.

Describe the solution you'd like
New feature with its own shortcut key: Allow shell commands and scripts to modify the current clipboard entry. Starting with text, and maybe later include copied images.

Additional context
This will make Pano more useful to Linux power users.