New pipeline(s) CLI argument

[daveaglick]

By default all pipelines are executed. It should be possible to specify specific pipeline(s) to execute, which will execute only them (and their dependent pipelines once pipeline parrallelism/dependencies are implemented in #189). You should be able to specify one or more pipelines to run.

Pipelines should also be able to specify that they shouldn't be run by default. That will allow special pipelines that only get run when the pipeline CLI argument specifies that they should.

[daveaglick]

Pipelines probably have three states when it comes to explicit pipeline execution:

• Default (runs when specified or during a normal run)
• Manual (only runs when explicitly specified)
• Always (always runs, even when not explicitly specified)

[daveaglick]

Done!