Move functions in ObjectJsonHelpers to their relevant namespaces and classes
- Move ParseColour to Colour::FromString
- Move ParseCursor to Cursor::FromString
- Move LoadStrings to StringTable::ReadJson
- Move LoadImages to ImageTable::ReadJson
- Move ParseObjectEntry to Object::ParseObjectEntry
- Move GetString, etc. to Json::GetString, etc.
- Delete ObjectJsonHelpers .cpp and .h files
Clang-format sees the text behind `#pragma region` as code and formats it. Instead of stating the copyright and date there, it's now in the comment block right below it. The text "Copyright" is left in the `#pragma region` line, as clang-format sees it as a single identifier.
I took the opportunity to normalize the dates, and add the copyright notice to the source files where it was missing them (except for third-party and the generated resources.h file).
