- improved statfs system call
 - intercepted statvfs library call

Both of the above function now report the aggregated real size
of all the data-nodes.

You can test this with `df "/tmp/gekkofs_mountpoint"` command

Implemented all the logic to handle truncate operation.

Test: added truncate test

margo, argobots and mercury have been updated. The abt-snoozer dep
required by margo it is not needed anymore.

RocksDB has been also updated to the lastest release

Instead use margo_iforward. Also only two bulk_handles are now used:
1 for margo_ipc and one for margo_rpc RPC requests.

Only use 1 segment now but with multiple transfers

We need to be explicit about I/O as it cannot be simply repeated. A response
from the daemon will come eventually, either success or failure.

- Previously the directory hierarchy was not clear regarding to which
  file belong to which part of the project (client or daemon).
  Further, we will have other clients in the future (such as Fuse).
- CMake files now differentiate between include dirs for all targets
  and target specific ones.
- Removed duplicate -pg flag.
- Not listing header files when adding executables or libraries
  is considered bad practice. Note that include_directories() is adding
  include paths to the code while adding all files used for executables
  and libraries provide the context which files belong to each binary.
  When only include_directories() is set, CMake assumes that all files
  belong to a binary (which is not necessarily true). As a result,
  some IDEs may break as the do not support this assumption.

  In general we should almost always favor explicitness over implicitness.