This makes the beginning of all files the same and a little simpler.
`${0%/*}` turns "/home/user/repository/bin/blackbox_edit" into
"/home/user/repository/bin", exactly like basename but without eating a
process.
Because other scripts needed `$blackbox_home` I made this into a
standardard variable that's always available.
This also loads _stack_lib.sh always because _blackbox_common.sh
requires it.
This solves some TODOs by moving shared code out into
`_blackbox_common.sh`.
New VCS commands were added, `vcs_ignore` and `vcs_notice` (the
opposite of ignore).
Made some utility functions
* `remove_filename_from_cryptlist` - The opposite of `add_file_to_cryptlist`
* `remove_line` - Removes a single line from a text file