Adds feature to modal to control remote caching behavior

Adds feature to modal to turn off caching of the modal content for
a remote modal.

- Adds option cache to modal options (default is true which
is the same as the current implementation)
- Setting cache to false will cause the remote modal content
to be loaded again after it is hidden and shown again.

This feature allows the use case for dynamic remote modal content that
needs to be refreshed each time the modal is shown, such as from a grid.