specify location relative to HOMEDIR for sqlite DB

Was getting this error on install:

    TASK: [notifier | syncdb]
    *****************************************************

    <--snip-->

    "/opt/wwc/notifier/virtualenvs/notifier/local/lib/python2.7/site-packages/django/db/backends/sqlite3/base.py",
    line 278, in _sqlite_create_connection
        self.connection = Database.connect(**kwargs)
    sqlite3.OperationalError: unable to open database file

    FATAL: all hosts have already failed -- aborting

Best to put somewhere, relative to HOME seems as good a place as any.
specify notifier_db_dir as a setting
add setting for EMAIL_USE_TLS

Default for this should be False, but allow that to be settable by
config.
Merge pull request #3 from edx/sef/fix-sqlite-location

Config by environment: sqlite DB location, email_use_tls