optionally keep install history
This adds the functionality for keeping the install/uninstall history along with a preference to enable it as a custom build option for allowing another app to read it. Keeping the history has many uses, including:
- "popularity contest"
- displaying install history locally in F-Droid
- reporting to IT device manager for tracking activity for malware, etc.
This is ready to be merged, but it is based on !386 (merged), so its marked WIP.
@dschuermann this touches some of your architecture, please review :)