Allow configuration centralizion in HDF5 files.

Allow configuration centralizion in HDF5 files.

Before this commit, each bump/temperature/vibration measurement needed
it's own local copy of the configuration.  This is good, because it
allow you to store experiments where the configuration changes between
measurements (e.g. one bump with push depth of 200 nm, followed by
others with a push depth of 300 nm).  However, such per-measurement
changes should be a rare occurrence, so this commit allows you to
specify the measurement configuration in a central location.  For
example:

  /bump/0/config/bump/...
  /bump/1/config/bump/...
  /bump/2/config/bump/...
  ...

can now be consolidated to

  /config/bump/...

If you want, you can still override the central config for a
particular measurement by placing the config in the old location.