Change default value of -q to none (None)

[BoPeng]

Currently we have a somewhat confusing default value for -q, basically,

1. If left unspecified, we use localhost as the default queue, which is by default a process queue but can be PBS queue as well.
2. If we set -q none, the tasks are handled as part of substep and no queue is used.
3. if we set -q host, we use host, and -q localhost is allowed.
4. Under a cluster environment, we say the default is -q none.

Because unspecified -q is usually understood as -q None, the selection of default value seems to be confusing. It would perhaps make more sense to

1. If -q is unspecified, namely if a None queue is specified, we disregard task keyword.
2. For the use of any queue, even localhost, -q is needed. This is the point of change where -q localhost will be needed for all our examples that use localhost.

I feel that this is more consistent and we do not need to have different default behavior for cluster and non-cluster environments.

[BoPeng]

Another side effect is that in SoS Notebook, workflow with task will have to be executed with %run -q localhost, or task: queue='localhost'.

[BoPeng]

@gaow I have released sos 0.19.15 with this change. Note that this change is backward incompatible but you should be fine because you mostly use -q explicitly.