[FIX] Fluid (Core): Set controller context only if not null. This needs to be done for rendering contexts without a controller context  (e.g. in a service)
  [TASK] Fluid (Core): Fixed a few doc comments
  [TASK] Fluid (Core): Removed commented-out code as it was obsolete

other changes in tx_fluid:
  * AbstractFormViewHelper: Removed persistenceManager-dependency. getName() and getValue() now return correct values for domain objects. Resolves #3651
  * Adjusted doc comments of ImageViewHelper. Resolves #3394
  * Fixed a few more doc comments