Remove use of namespace packages in PyUtilib

[jsiirola]

Fixes: #N/A

Summary/Motivation:

Removes the use of namespace packages from pyutilib. After we consolidated the bulk of PyUtilib into a single repository, there aren't (maintained) pyutilib capabilities outside of this repository. Removing the namespace packaging simplifies several things (including plugin imports)

Changes proposed in this PR:

• remove namespace packages pyutilib and pyutilib.component

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[coveralls]

Coverage decreased (-0.06%) to 61.062% when pulling 37a8c89 on jsiirola:remove-namespace-packages into f61be88 on PyUtilib:master.

[jsiirola]

@whart222: please take a look at this and see if you agree. This is a rework of #82 to only include the part related to the removal of the namespace packages.

[whart222]

@jsiirola I think this looks OK. This also includes deferral of some logic w.r.t. egg plugins for pyutilib.component. I think you should add documentation about that change to the PR, but I don't think we need to separate that into a separate PR.

FYI, I looked at the other pyutilib.* packages hosted on PyPI, and I checked if they are actively being used within GitHub projects. I couldn't find any, and hence I think there's minimal risk that this change will be disruptive for PyUtilib users who may be pulling-in multiple PyUtilib packages and relying on this namespacing feature. Further, those packages are quite old, so I would encourage users to discontinue their use in any case.

[whart222]

I added comments separately. I'm not sure if the coverage checks are meaningful, but the code changes seem fine.

[jsiirola]

I added some (minimal) documentation for the deferred import of pkg_resources in the Egg loader.