GeoTecINIT/nativescript-task-dispatcher: Improved sticky notification icon options

This release does not contain any breaking changes

With this release we bring better sticky notification icon options. Concretely, it allows some degree of customisation:

• If Android version is 5 or above, the plugin will search for a drawable named: ic_stat_notify_silhouette, and will use it if available.
• If that condition is not met or the drawable does no exist, it will try to use a drawable named: ic_stat_notify.

Otherwise, it will use the app icon as it was doing before.

We follow the same defaults that the @nativescript/local-notifications does, making the compatibility between the two seamless.

We don't allow yet to set a custom icon. We think that the options we offer will suffice almost all the posible use cases. But, anyway, if you need to specify a custom icon for a certain reason, please, feel free to open an issue to discuss about the details of your request.