launch: more configurable and fixes.

It's now possible to configure browser and terminal commands.

The terminal doesn't default to execute "sh -c" anymore so a lot of error prone quoting
was removed.
hist: configurable path and cleaner purge.

The history file path can now be configured by setting the env var HISTORY.

The purge operation filters duplicates before droping the history n-tail.
search: browser is now configurable.
status: explicit configuration section.
xinitrc: portable->nm-applet, clean up.