Draft: add dbus service and secure item

This is a draft merge request to compare with this Work in progress.

This fork introduce Secure Item, it is a feature I introduced in clipman from a personal need, the goal is to hide item content in clipman history when sending password to the clipboard.

All details are explained in the gitlab fork README_secure_item_dbus.md.

The open issue that relates to my need was: clipman issue #25.

The secure item are them removed automatically from clipman. Though, for more versatility it's done outside clipman code from the cli in bash example script I wrote. This fork also introduce DBUS API that allow to modify clipman history in memory trough DBUS call. All are wrapped inside clipman_cli.sh helper.

This is a huge refactor, that still have bug in circular indexes and use a some shell script for the clipman_cli Proof of Concept.

All comments are welcome.