Basic select_regions command

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There should be a more basic version of the _selectregions command exposed via the API. If the user knows all experiment IDs/names, then something like:

server.select_experiment_regions([list_of_names], None/chrom, None/start, None/end, user_key)

would be more convenient than the current one:

server.select_regions([list_of_names], None, None, None, None, None, None, None, None, user_key)