Add initialize function to fsapi

[MichaelPesce]

Fixes/Resolves:

• adds a hook for flowsheets to provide an optional initialize function to the UI

Summary/Motivation:

The parameter sweep tool (see UI PR#103) with parallel capabilities allows for an optional initialize function. in the case that there is no initialize function, it runs the build function multiple times. This takes a long time. If the UI can access a models initialize function, then parameter sweep run times can be decreased.

Changes proposed in this PR:

• update fsapi to allow for a do_initailize function

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[dangunter]

I think it makes sense with the suggested changes. I need to look it over one more time though, maybe the initialize internal method can be dropped entirely, not sure.

[dangunter]

LGTM