[vauvenal5]

Here is the first split out PR for add photos app. It contains an extension of the neon_framework to support app_capabilities.

This way apps can propagate certain functionality to other apps or the neon_framework without the need to add all of their code to the framework itself.

The upcoming PRs will contain two examples for this:

• photos_app: exposing a gallery view where you can swipe through images
• files_app: exposing the directory selection dialog for selecting a directory as an option

[vauvenal5]

@provokateurin I rebased this PR and believe it is ready for review.

Regarding the contents, I remember we had a general discussion between this vs moving stuff into the framework.

This PR basically gives the framework cross app communication abilities without the need to move everything into the framework. Two examples from my use cases are:

• the ability to open a directory chooser dialog from options
• the ability to jump into image view screen directly from files app

The idea is to keep the framework more lightweight and give developers the choice to keep their mobile apps light weight if they do not need certain features.

One open question, is the naming okay or should we look for something else? AppCapabilities and the Server-Capabilities are pretty close and could be confused.

Off-topic: Do you have an idea what's going on with the Codecov setup step?