Out of sample MuG to Vec

[hhelm10]

Is your feature request related to a problem? Please describe.

For classification problems it is important to be able to learn a vector representation of the graphs without necessarily including the test data.

Describe the solution you'd like

A transform method added to the Mug2Vec class so that previously unseen graphs can be embedded in the previously learned space.

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Provide references (if applicable)

If your feature request is related to a published algorithm/idea, please provide links to
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Additional context

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