Adds keyboard bindings and associated help menu for selecting reminder type in bookmark modal, and pressing Enter to save.
Introduce the following APIs for `KeyboardShortcuts`:
* `pause` - Uses the provided array of combinations and unbinds them using `Mousetrap`.
* `unpause` - Uses the provided combinations and rebinds them to their default shortcuts listed in `KeyboardShortcuts`.
* `addBindings` - Adds the array of keyboard shortcut bindings and calls the provided callback when a binding is fired with Mousetrap.
* `unbind` - Takes an object literal of a binding map and unbinds all of them e.g. `{ enter: { handler: saveAndClose" } };`
