Replace table based panes (build queue, build executors, build history) with a div based approach

This PR changes how `<l:pane>` renders.

The table (containing the "data") is now wrapped in a `<div>`.  The pane title/header is now done using a `<div>` and the `<l:pane>` tag now also supports a "footer" attribute, which works similar to the "title" attribute (i.e. can receive markup).

`<l:pane>` can now also take a "class" attribute which gets mapped onto the inner data table and can be used to apply styles.