set cursor style as pointer

On Firefox, { cursor: inherit; } was resolving to 'auto', displaying as
'default' instead of 'pointer'.
linting fixes
add 'initialized' public variable (for debugging)
fix drawer-reset structure

The previous structure prevented children elements from naturally
inheriting properties from their closest parents. This is because the
selectors defined here would exactly match each child element.

The problem is that we weren't properly segmenting between inherited and
non-inherited properties. For inherited properties, we need to reset
them by setting them all to 'inherit', then apply the desired default
values to the top-level betterlink-drawer.
only allow root initialization once
add function to explicitly provide image directory

This is needed when locally testing betterlink-interface on external
sites.

There needs to be a way for the local Chrome Extension to inform
betterlink_user_interface where the files are served from. This isn't an
issue when using the provided example_site.html because it's being
served from the same location.
fix race condition for initializing betterlink

Check repeatedly for 12 seconds if betterlink_user_interface has fully
loaded. Once it has, *then* excuteInitListeners.
display images when externally testing local code

When using the Chrome Extension to locally test
betterlink_user_interface, images would fail to load because the
directory wasn't updated to reflect local hosting.