fix(cpn): ModelData usage due to introduction of complex data types

[elecpower]

Summary of changes:

• the use of std::string data type required reworking ModelData struct initialisation
• housekeeping including renaming class customSwitch to CustomSwitchData

Thanks to @philmoz for his contribution for custom screen data work, diagnosis and solutions

TODO:

• initialisation
• copy constructor
• assignment operator
• copy, cut, delete and paste ui functions