Group: add findByNameOrAttribute method
[test] Group: add test for findByNameOrAttribute
Group::findByNameOrAttribute: add doxygen docu
Group: small cleanup: use make_optional
Group: findByNameOrAttribute -> findGroupByName..
Group: findGroupByNameOrAttribute: swap params

To be consistant with the other FindXByY functions
File+FileHDF5+tests: getBlock support for name&id
Block+H5+test: getDataArray: support for name+id
Merge pull request #399 from gicmo/nameOrId

Initial support for opening entities by name or id