Properly encode the e-mail headers and body

Properly encode the e-mail headers and body

The headers are QP-encoded and the body is left as utf-8. The mail command
now uses the email Python package for setting the headers and encoding. The
template files were modified as there is no need for "Date:" and
"%(endofheaders)s".

Signed-off-by: Catalin Marinas <catalin.marinas@gmail.com>