Electrum needs either "cryptography" or "pycrytodomex" (since #6014).
Previously we have been using a custom fork (of ours) of pycryptodomex,
now let's just use upstream "cryptography".
- updated p4a pulls in newer openssl (old one is no longer available from openssl.org)
- old NDK no longer available (new one is what updated p4a recommends)
- also merge https://github.com/kivy/buildozer/pull/957 as prereq for
building multiple apks (one per arch)
- and custom buildozer commit to put target arch into apk name
old p4a did not work with new buildozer. kivy master crashes.
kivy latest release has runtime issues (orientation was landscape).
these versions seem to work.
also updated dockerfile to more closely match p4a master.
