More refactoring of how keys, passwords and secrets are stored

includes a working loopback and tempfile cleanup in endgame()
and several changes in order to avoid saving anything on disk
WIP addressing #124 and #126
small fix to tests
Cleanup and normalization of functions handling secrets

also now using a dash - after print and gettext options to avoid
parsing printed strings as options.
More cleanup and refactoring.

Now most functions are stable. tomb open -k image.jpg can use images
directly as keys, works on tests, but needs more debugging.