Changes in CVariable and CVariableTemplate:
Replace CVariable with CVariableBase
Replace CVariableTemplate<> (it's obvious) with CVariable<>

Added file functions/GroupFunctions.cpp for helper functions to
decongest CGroup, especially those related to variable and transport
selections from lookup table structs (see SSupport.h).

Added exception to "using" in doc/CodingGuidelines

Switched all shared_ptr in CGroup members to the more restrictive
unique_ptr

To-do:
Modify CGroup and SetMembers in ADIOSFunctions so groupName is
identified before CGroup. This will allow an emplace on m_Groups map for
unique_ptr.