[PropertyAccess] Refactored PropertyAccessorTest
[PropertyAccess] Refactored PropertyAccessorCollectionTest
[PropertyAccess] Added isReadable() and isWritable()
[PropertyAccess] Fixed CS and added missing documentation
[PropertyAccess] Removed the argument $value from isWritable()

To keep isWritable() and setValue() consistent, the exception thrown when only
an adder was present, but no remover (or vice versa), was removed.
[PropertyAccess] Added missing exceptions to phpdoc