[TASK] Various cleaning in FluxService

It's cleaning time - fixing a few boolean/null comparison orders and implements a previously unified API method, having the side benefit of also respecting the cache in one additional case: when reading a list of available content areas from a content element by UID (which happens when pasting content elements).
[TASK] Remove a superfluous internal cache use
[TASK] Save a few µs by returning an array original instead of copy
[BUGFIX] Consider recursive array of values in cache key
Merge pull request #97 from NamelessCoder/servicecleanup

[TASK] Service cleanup: CGL, shifts to API, mini performance boosts