Reduce app size by outsourcing images

[Robbendebiene]

Currently the app uses about 50mb of storage just for photos. This is is about 70-80% of the total app size.
We probably should outsource the images to a server or github repository in combination with a local caching method like: https://pub.dev/packages/cached_network_image

Doing so would require an adjustment of the privacy policy.

[7h30n3]

I think before making a decision and implementing that feature we should list the pros and cons (for different use cases).

[Robbendebiene]

Some generel pros and cons:

Pros:

• scalable
• images can be updated without releasing a new app version
• images from other websites/hosting providers can be used
• potentially reduced storage, because not all images from the entire question catalog must be downloaded
• faster app download/install/update

Cons:

• requires additional images hosting provider
• high chance of downloading images over cellular network instead of WiFi
• increased image loading delay for the first time an image is displayed

[7h30n3]

Issue was mitigated with #328.