Allow drop-in browser profile in {/etc,$XDG_CONFIG_HOME}/psd/browsers/

[Freso]

I note that the response to several requests of support for new browsers is to copy an existing profile and modify it for the browser in question (or symlink one from the contrib/ directory). AFAICT the only way for psd to pick up this profile is if it’s located in /usr/share/psd/browsers/.

Since people shouldn’t put local configuration in /usr it would be nice if psd would either look in /etc/psd/browsers and/or $XDG_CONFIG_HOME/psd/browsers/ for additional browser definitions – maybe the latter if it continues to be a user-service, but maybe the former if you want to go the path of starting as root and then dropping to an unprivileged user as you have discussed in some of the security oriented issues.

A bonus would be if a file exists in $ETC/psd/browsers/ that shares the name of one in /usr/share/psd/browsers/ it would then override the /usr one (similar to how e.g. pacman hooks and systemd service files work).

[graysky2]

PRs are welcome