Move classes into separate files

FossilOrigin-Name: 14861826d4c1f561aca909afe773366a46b57b20cf41fd668092dfb98d960d80

src/KeyMapping.m

@@ -0,0 +1,13 @@
+#import "KeyMapping.h"
+
+@implementation KeyMapping
+- (instancetype)initWithCode:(int)code name:(OFString *)name
+{
+	self = [super init];
+
+	_code = code;
+	_name = [name copy];
+
+	return self;
+}
+@end