do not put timestamps in javadoc-generated files

This aids reproducible builds: besides the timestamp, `javadoc` will create
the exact same files across different machines, java versions, etc.
find path to set ndk.dir, if ndk.dir is not set already

One standard way of setting ndk.dir is to set it in a .properties file. If
that has not been done, then this ant code looks for the env var
ANDROID_NDK and the path where ndk-build is installed.

ndk.dir is not currently used by the build system, except to write out info
to the manifest about the build environment.
methods for handing raw key directly to sqlite3_key() and sqlite_rekey()

This provides methods for handing the raw AES key data directly to
SQLCipher, skipping SQLCipher's key derivation process. This allows an app
to make their own key derivation process.  This is how we already handle
things with CacheWord, which uses 32 random bytes for the raw key, then
manages sending that raw key to multiple things that need to be unlocked
(SQLCipher-for-Android, IOCipher, RSA keys, etc).