Let the user know when notifications are being fetched

[ilmotta]

Feature Issue

User Story

As I user
I want to know when notifications are loading
So that even in slower connection scenarios I know the app is working properly

Notes

• Pull to refresh might not be necessary to implement, due to the fact that the AC state is already kept up-to-date using a polling strategy (see namespace transport.message.core).
• Skeletons are probably the way to go, but this should be double-checked with the design team.
• Animations are also open for design analysis, for example, when a new notification arrives and is inserted at the top.

[cammellos]

I will move this to a discussion since it requires design input