Fractal demo: Added configuration UI for load balancer IP address

Updated user_data to support converting 'list' typed parameters to/from comma separated strings.
Tweaked .gitignore to re-include lib/ directory.
Added HTML hover text to show the configured load balancer IP address.
refactor (DRY) to use _get_lb_servers() everywhere
Merge pull request #12 from GoogleCloudPlatform/fractal-config

Fractal demo: Added configuration UI for load balancer IP address