stream get and put through pipes instead of the bus

the bus has a hard time handling the amounts of data we may conceivably be pushing over it (gibibytes... literally). to mitigate enormous performance problems push the data through a pipe instead and only pass the unix socket over the bus. this is a bit more code and a bit crappy posix-y one at that, but it's heaps better than hogging the system bus and perhaps even get stuck because of problems in qdbus with large dbusmessages.

CCBUG: 468673