[UX] Enhance notifications management

[juliensl]

Hello!

Describe the feature you'd like

Currently, we can choose to have notification on our phone for "every messages", "messages with mentions" or "nothing". It's already a good thing, but I thing we can enhance the "every messages" option.

When you choose this option, and be on a channel with 300 or 400 messages each day, your phone will make noise/do vibrations 400 times in the day.

I think we can enhance it to have a notification management like on messenger or Whatsapp, I mean, have a notification when a message is send on a channel, but not have notifications after until you read the messages.

Example:

1. A message is sent on the channel, I've got a notification
2. I not read it now
3. Other messages are sent on the channel, I don't have more notifications
4. I read them and close
5. A new message is sent on the channel, I've got a notification
6. ...

For different channels:

1. A message is sent on the channel A, I've got a notification
2. I not read it now
3. Other messages are sent on the channel A, I don't have more notifications
4. A message is sent on the channel B, I've got a notification
5. Other messages are sent on the channel A or B, I don't have more notifications

On the Sony xperia X compact, the fact of receive too much notifications makes it be slow and have bugs :/ ( @eric-burel )

Devices and Versions

Your Rocket.Chat.Android version: 3.5.0 (2074) Your Rocket.Chat Server version: 1.1.3

Mobile device model and OS version: (e.g. "Nexus 7 - Android 6.0.1")

1. Samsung A3 2016 - SM-A310F - Android 7.0
2. BQ Aquaris U2 - Android 7.1.2
3. Sony xperia X compact - Android 7.1.1

What do you think ? :)