Fixes #703502 by porting zeitgeist-dp plugin to zeitgeist-2.0

This drops the libzeitgeist dependency and replaces it with
a zeitgeist-2.0 dependency ≥ 0.9.12.

Closes: https://bugzilla.gnome.org/show_bug.cgi?id=703502

Signed-off-by: Manish Sinha <manishsinha@ubuntu.com>