Fix warning: 'synfigapp::Action::Group::set_param' hides overloaded virtual functions
Fix wrong header guard macro
Fix warning: logical not is only applied to the left hand side of this comparison
Fix warning unused variable
Fix warning: comparison of integers of different signs: 'int' and 'const size_type'
Fix warnings of unused variables
Fix improper use of class token
Fix warnings: Function ... hides overloaded virtual functions