feat(uibootstrap-modal): add basic modal service and template when using uibootstrap

Changes: (only if ui-bootstrap is selected)
- add `client/components/modal` folder
- modal folder contains service, markup template, and stylesheet
- modal service is intended to be extended, comes with `Modal.confirm.delete()` method
- admin and main page will both use `Modal.confirm.delete()`

Todo:
- possibly extend the modal service to include a basic alert class?
- review code for cleanliness and correctness
- write test for `Modal` service?