[Scenario] Use JButton for Activity Type link

Use JButton instead of JLabel for the clickable
icon used to follow links to external resources.
This supports tab focus etc.
[Scenario] Open browser on button click

Follow the provided resource link by opening
a browser, if possible, from the Activity Type's
Info View.
[Scenario] Silently ignore bad URLs

User experience for this situation is TBD
[Scenario] Notify Info View of changes to URL field

When an Activity Type's URL field is edited
(completed by either focus change or enter)
notify the info view, which is connected
via a change listener. This allows the change
to be persisted along with the component.
[Scenario] Show dialog message on bad link
[Scenario] Move strings to bundle for Activity Type

Move strings used in the custom Info View UI for
Activity Type to a bundle.
[Scenario] Add tooltip to URL-opening button

Add a tooltip to the button used to open
linked resources from Activity Type's
Info View.