webstaff: add egJsonExporter directive
This directive is used to allow a piece of JSON
to be saved to the user's filesystem. For example:
<span eg-json-exporter container="foo" default-file-name="example.json">Export</span>
specifies a button that, when click, allows the user to save
the contents of the scope variable foo. The dialog that
appears will use "example.json" as the default filename.
This also adds a new dependency, the MIT-licensed
angular-file-saver service written by Philipp Alferov:
https://alferov.github.io/angular-file-saver/
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>