[TYPO3-core] RFC #11684: Add support for flash messages in the backend

[Steffen Kamper]

Hi Ingo,

i like the flashMessage and it's a good way to collect messages from 
different places.

What i mislike is that i have to instanciate it for each message. 
Shouldn't it be a singleton instead which collects all the messages?

I have my pageRenderer in mind where you could simple add those 
messages, and you could also use it in FE.

vg Steffen