MODE-1816 REST v2 responses base property representations on number of values

The response should base the field value for a given property based upon
whether that JCR property is single-valued or multi-valued, not upon
the number of values. If multi-valued, then the field value should be
an array (even if there is just one item). Version 1 of the REST API
already works this way, but the version 2 was changed.

Note that it is still possible for property representations in
requests to use a single value (rather than an array) when setting
a multi-value to a single value, or the more conventional practice
of using an array to set a multi-valued array. The latter is obviously
required when setting the mutli-valued property to 0 or 2+ values.

Several of the expected results were incorrect and have been changed.