Implements customization for the indicator as proposed in #2788 with comments from #3367 in mind.
The default behaviour does not change exept for the caps lock text color.
This involves setuid'ing swaylock, which then forks and drops perms on
the parent process. The child process remains root and listens on a pipe
for requests to validate passwords against /etc/shadow.
- Replace char* with static array. Any chars > 1024 will be discarded.
- mlock() password buffer so it can't be written to swap.
- Clear password buffer after auth succeeds or fails.
This is basically the same treatment I gave the 0.15 branch in https://github.com/swaywm/sway/pull/1519
Colors are configured through the command line so that swaylock conforms
to the i3lock fork 'github.com/chrjguill/i3lock-color'. Differences from
it are that one letter options '-r' and '-s' are not implimentend because
'-s' is already used by '--scaling' in swaylock.
This commit also fixed whitespace in 'include/swaylock/swaylock.h' and
changed `parse_color` in 'common/util.h' so that it can accept colors
that do not start with a hash. This was done to keep compatability with
the i3lock fork.
