listruns() should get db from session if possible

[prjemian]

When using an intake-style catalog, the listruns() defaults through to an existing mongodb_config instead. Make this smarter (but not at the expense of more fragile).

[prjemian]

Use get_ipython() (if successful) to get db from the environment if both db and cat are not given as kwargs.

[prjemian]

A challenge is to identify the best database to who with listruns(). Thus, listruns() should report the name of the database it is reporting.

[prjemian]

It is observed that when Broker-style yaml files are opened with db = databroker.catalog["db_name"] (for example), the configuration name reported by db.name is None instead of db_name. This should be addressed in upstream databroker package.

In [222]: mdb.name

In [223]: mdb2 = databroker.Broker.named("mongodb_config")

In [224]: mdb2.name
Out[224]: 'mongodb_config'

In [225]: mdb = databroker.catalog["mongodb_config"]

In [226]: mdb.name

[prjemian]

Tough to report the database name since the output of listruns() is a pyRestTable.Table() instance. Could implement when printing=True.