New app: Bits & Bäume 2018. (conference in Berlin at Nov 17-18)

• The app complies with the inclusion criteria
• The original app author has been notified (and supports the inclusion)
• All related fdroiddata and rfp issues have been referenced in this merge request
• Builds with fdroid build

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I tried the local build with fdroid but the process fails with the following error:

AttributeError: cffi library '_openssl' has no function, constant or global variable named 'Cryptography_HAS_SIGALGS'

The problem seems to be an outdated Python3 module (cryptography) on my machine. I run Ubuntu 16.04 and could not yet figure out how to install and provide the required version for the fdroid build.
Nonetheless, I could successfully build the same commit with Gradle. It is already published on Google Play. Therefore, I expect no problems with the build on fdroid.org.