Add vote and votes methods to `ICompetitionSuggestion`

Would be nice if `ICompetitionSuggestion` contained the vote and votes methods. I guess this is an effect of how the client lib entities are architected in general, where entity's static and dynamic properties are stored in class fields rather than the class itself, whereas the entity methods are stored elsewhere in the class. This is awkward for the user to code and not intuitive as it does not follow the usual object-oriented design pattern everyone is used-to.

Locate the ICompetitionSuggestion interface and the existing entity method definitions in the client library. Compare how static and dynamic properties are separated from entity methods, then determine how vote and votes should be exposed consistently. Done means users can call both methods directly through ICompetitionSuggestion without working around the current class-field architecture.

Written by the indexing model from the issue text.