Add missing type declaration for several defcustom forms as well as group declarations.
This removes the byte-compiler warnings and inhance user experience.
Coverage remained the same at 100.0% when pulling eedbcb624b9a9b653d70855ede9538c9e7c79c54 on pierre-rouleau:master into 9565eeaa1d26bc0ab83eb65bd30470888f724044 on ardumont:master.
Add missing type declaration for several defcustom forms as well as group declarations. This removes the byte-compiler warnings and inhance user experience.