Start using the previews from the server

[nickvergessen]

• API should return the mimetype as well, so the clients can use their local mimetype icons if available
• API should return path + id so apps can link to the file locally instead of redirecting to the browser
• Readd onClick handler (local when available otherwise browser (trashbin))
• Kill setBitmap after local mimetype icons are used

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• Requires Add activity previews android-library#73

[tobiasKaminsky]

@nickvergessen do we want to finish this during hackweek (we/thu)?

[nickvergessen]

I dont think I got time

[tobiasKaminsky]

@nickvergessen once the activity API returns mentioned parts (mimetype, fileId, …) please re-open or create an issue, so that we can develop this.
Keeping this old PR just causes overhead while trying to keep it up to date.