Don't Throw Error for Empty Requests

- add empty group signature
- prettify log output (spaces)
Allow clock systems for domain offsets

If the domain offsets are ordered in a clock system instead of
starting with globalDomain.getOffset() (could be at (0,0,0) )
at file (0,0,0), this patch allows to read them.

First, the file with the lowest offset (aka
globalDomain.getOffset() ) has to be found. Afterwards,
the same divide&conquer algorithm looks for the top-left corner,
but only in the "upper" or "lower" volume, seen from the "first"
file.

At the end, the real read algorithm will walk over an "optimal"
number of files for requested planes. If no plane was requested
but a general volume, the algorithm (should) still work but is
less efficient if one is not looking for the full domain
(same behaviour as before).
Clearify Vars and Comments
Merge pull request #41 from ax3l/fix/movingWindow

Fix/moving window
Allow to write NULL data

 - allow NULL when writing (only create dataset)
 - add subtest in SimpleDataTest
Allow NULL data in append calls
Fix exception messages
Verify size when reading empty dataset
Merge pull request #43 from ComputationalRadiationPhysics/fix_null

Allow to write and append NULL data
Rename DCollector:: to splash::
Merge pull request #45 from ComputationalRadiationPhysics/nm_splash

Rename DCollector:: to splash::
Added version header

 - can test for SPLASH_VERSION define
Allow to attach attributes to iterations

 - modified read/writeAttribute
 - added test in AttributesTest
Remove deprecated parameter check
Fix searching in DomainCollector

 - set running variables to break from while loops
Merge pull request #49 from ComputationalRadiationPhysics/fix-search

Fix searching in DomainCollector
Change versioning in version.hpp
Add check for valid but empty names
Merge pull request #48 from ComputationalRadiationPhysics/new-attr

Allow to attach attributes to iterations
Merge pull request #50 from ComputationalRadiationPhysics/cmake-version

Add version.hpp header