Generated AppWidgetset and serialization

[vaadin-bot]

Originally by lrozenblyum

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AppWidgetset generated by maven plug-in causes eclipse generating warning about serialization (after Eclipse : Maven -> Update project...) :

-The serializable class AppWidgetset does not declare a static final serialVersionUID field of type long* in target/generated-sources/wscdn

(surprisingly eclipse validates target directory as well).

Ideas to fix:

1. Make com.vaadin.server.WidgetsetInfo interface not Serializable (not sure if it's really needed to be Serializable)

2. Make vaadin-maven-plugin generate new serialVersionUID inside UpdateWidgetsetMojo.java)

If you approve one of ways of fixing the problem, I can contribute a patch.

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Imported from https://dev.vaadin.com/ issue #20241

[vaadin-bot]

Originally by lrozenblyum

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Another option:
3) Modify widgetsetinfo.tmpl inside maven-vaadin-plugin
by adding

@SupressWarnings("serial")