ui: Reimplement using python

* As always, a simple shell script grows large and becomes a PITA to
  handle string arguments and forking.  It typically ends up re-written
  in python.  That happened.
* The -f flag never worked with ssh as it redirects stdin from /dev/null
* ui_copy now uses python now buffers the entire stdin string before
  forking and waiting in the case of copy.
* ui_paste was replicated just to be consistent.
* fssh will likely be re-written too in the future when needed.