Required dependencies missing from debian/control

Just watching your FOSDEM talk (which was excellent BTW), so took a look at the project.

After generating a debchange file I ran ```dpkg-buildpackage -b``` (very happy to see that /debian directory) and noticed that the ```python2.7 setup.py build``` command failed on a python-jinja2 error. Installing the package fixed it, so I figure this should be listed in control. It also seems required to run the mailpile command shell.

Further, the mailpile command shell ```setup``` command suggested to install spambayes, so we should probably add that suggestion to the control file also.

I don't know if there is a minimum required version of python-jinja2. If known, it can be added, but just mentioning it is an improvement. Tested on Debian GNU/Linux wheezy/stable.