Wait for completion of writes

Not doing so could result in garbage reads (in 0.3% of times).
Rates to rates for easy reading of queue stats
Version bump 0.6.25
Added warnings about dangling, unreferenced variables
libdata_array was placed incorrectly in grape-components, moved it to
grape (versionless link to grape-dev)
testerhead: added ping command and way to disable queue item acking
Concurrent runloop isolated into concurrent_pump.hpp

Added concurrent_queue_{writer,reader} classes.
New utilities queue-pull and queue-push make use of this abstractions.
Old queue-pump leaved untouched for now.
Adaptive flow control in the queue driver

Changed driver's flow control to follow both actual processing speed of
the app and peeking rate of the queue.
elliptics_client_state: get json doc by reference instead of value
Fixed queue crash on chunk data unavailability
Check chunks metadata availability on start, refuse to start if its not
Removed write waits again
Queue gained ability to run in one group and store data in the other(s)

Added storage-group setting overrides groups setting for queue data
accesses. Also added wait-timeout setting.
Little cleanup in log messages
Added concurrent_pump.hpp to grape-dev
Version bump 0.7.0
driver: fixed reaction to timeout errors
queue: fixed tight read repeat loop on "chunk data unavailable" error
indent cleanup
driver: {wait,check}-timeout and high-rate-limit settings