Don't download photos to local storage unless explicitly told to by the user

Actual behaviour

-Photos are downloaded to local storage, rather than cached.

Expected behaviour

-When browsing a directory of photos, I don't want to have to wait for each photo to be downloaded and stored locally before being able to view them.
-The behavour of video files is to stream them unless given the action to download. Photos should follow similar logic.

Steps to reproduce

1. Create a folder on a remote server and add photos
2. Navigate to the folder via the owncloud android app
3. Have you local storage fill up trying to just view the files in the folder.

Can this problem be reproduced with the official owncloud server?
(url: https://demo.owncloud.org, user: test, password: test)
Yes

Environment data

Android version: 8.1 Sept 5th patch

Device model: Nexus 6p

Stock or customized system: Stock android

ownCloud app version: 2.8.0

ownCloud server version: 10.0.8

Start by tracing how the Android app opens remote photo files and how it handles the existing video streaming behavior. Compare the photo and video paths, then verify that browsing photos does not persist them locally unless the user explicitly downloads them.