ImplContainer behaves like bool and like boost::optional

It compares to boost::none and has isNone() method now.
[test] Complete tests for DataArray

This is part of issue #25
DimensionHDF5: Fix broken switch (missing break)
[test] DataArray: Enhance Dimension tests
Just some whitespace fixes. No logic change.
Merge pull request #129 from gicmo/balint_new

ImplContainer optional semantics and DataArray tests
(merge & rebase by @gicmo)