Add Flask_Mail as a dependency of docassemble.base
Add Flask_Mail as a dependency of docassemble.base

It's used in `util.py:send_email`. With this addition, you can
install `docassemble.base` without installing `docassemble.webapp`, and
call (most) of the functions. Doesn't entirely work, but all of the dependcies
are present now.

jhpyle/docassemble,jhpyle/docassemble,jhpyle/docassemble,jhpyle/docassemble,jhpyle/docassemble