Clean up JS scripts

Minimize the exposure of private functions. This ensures that calls are
only using a public API and avoids polluting the global namespace with
uzbl variables.
Add an uzbl-util util script

This contains a function to print output more portably[1] and two
convenience functions for controlling uzbl itself.

[1]The echo command/builtin may or may not support the -n flag and
there's no way to prevent an implementation that does not support it to
not ignore the '-n' flag.
Use uzbl-util in download.sh
Use uzbl-util in follow.sh
Use uzbl-util in formfiller.sh
Use uzbl-util in go_input.sh
Use uzbl-util in history.sh
Use uzbl-util in insert_bookmark.sh
Use uzbl-util in insert_temp.sh
Use uzbl-util in instance-select-wmii.sh
Use uzbl-util in load_url_from_bookmarks.sh
Use uzbl-util in load_url_from_history.sh
Use uzbl-util in load_url_from_temps.sh
Use uzbl-util in session.sh
Quote shell assignments
Clean up the follow.sh script
Improve the formfiller script

Basically, the storing every profile in a single file was error prone
and hacky. The more unix-y thing to do is just store each profile in its
own file. This makes profiles much easier to handle.
Add a function to escape '@' for uzbl
Fix escaping in follow.sh
Log errors from JavaScript scripts