Remove unneeded cache resets of front-end code

[fweik]

Currently the whole particle fetch cache is dropped when any particle is touched. This is not needed, because in most of the cases it is know which particle is modified, so only that particle needs to be removed from the cache. For particle updates thru the messages, there is even a description of the mutation, so the updated can also be applied to the cache particle, and the cache can stay valid.

This leads to huge performance improvements when reading and then mutating particles in a loop.