feat(LocalNotifications): add createChannel, deleteChannel and listChannels methods

[dwlrathod]

Starting in Android 8.0 (API level 26), all notifications must be assigned to a channel. For each channel, you can set the visual and auditory behaviour that is applied to all notifications in that channel. Then, users can change these settings and decide which notification channels from your app should be intrusive or visible at all.

This PR is for allowing channel feature to LocalNotification. The first user needs to create a Notification channel with createChannel method and then assign channelId at the time of scheduling notification. If no channelId is provided will use the default channel and if provided channelId does not exist, the notification will not be generated.
Fixes #2675

[jcesarmobile]

First of all, when you create a feature request (issue or PR, you should provide a lot more information about what you want, why is good, how to use, etc.), this PR has no information at all other than a link to an issue with little information on its description.

By looking at the code, you are removing the default channel, I don't think that's good, one thing is allowing to use different channels, and another is to force using a channel. The channelId should be optional and use the default channel if an id was not provided. If not, this will break all existing apps.

The method on the manager should be listChannels, not listChannel

Also, you should add the methods for iOS too despite they won't work, they should do the same they do on PushNotifications plugin.

About the web, put the imports on top, not in the methods.

Finally, on the types, we put the regular methods before the addListener methods, you have put them after the removeAllListeners, can you move them up?

[dwlrathod]

@jcesarmobile good points. Hopefully, all are done.

Thank you for your time and help! 🙂

[jcesarmobile]

I've made a few changes, will merge once the tests finish.