Virtual states cannot be limited in memory usage

There has been done some earlier work on this issue, however it needs some sophistication to be useful (like configurable limits). Also, I am not sure whether we can actually use it through for example SPI. Until now, IIRC, we could not use it from HST2 pov:

See https://issues.onehippo.com/browse/CMS7-4174

Issue description:

The memory usage of virtual layers cannot be limited. This means, it can grow indefinitely. This also has to do with the way jackrabbit item state managers are constructed. Because of we cannot limit the memory in the repository. the HST flushes Jcr sessions every X minutes, as some sort of safety. However, this of course cannot avoid that still an OOM can occur. The HST cannot fix this properly.

It might be quite hard to properly tackle this issue in the repository, as all the virtual nodes are part of a change log in the HippoLocalItemStateManager's.

Ard