Fix #512 CLI config reset functions no longer work

Changed optional arguments --reset, --reset-configuration, and
--reset-database to become positional arguments underneath a reset
subparser.

Options are now "all", "configuration", or "database". For example:

    freeseer config reset all
    freeseer config reset configuration
    freeseer config reset database

Added unittests for reset, reset_configuration, and reset_database
functions from util.py.

Fix #465
Signed-off-by: Thanh Ha <thanh.ha@alumni.carleton.ca>