fix(ngResource): don't convert literal values into Resource objects when isArray is true

Previously non-object literals would be thrown out of Resource responses with isArray===true, or otherwise converted into Objects (in the case of string literals). The reason for this is because shallowClearAndCopy iterates over keys, and copies keys into the destination. Iterating over String keys results in integer keys, with a single-character value.

Not converting non-objects to Resources means that you lose the ability to perform Resource operations on them. However, they become usable as strings, numbers, or booleans, which is important.

In the future, it would be useful to make these useful as Resources while still retaining their primitive value usefulness. (@rodyhaddad can you think of a way to do this? You're the master of ES5 valueOf, as far as I know :P)

Closes #6314