Fix imports in Kotlin model generation

The models project generated Kotlin code that didn't have the correct imports. This happened because the imports were not being tracked as imports in the KotlinCodeGenerator, only as code.

jte-kotlin/src/main/java/gg/jte/compiler/kotlin/KotlinCodeGenerator.java

@@ -48,6 +48,7 @@ public KotlinCodeGenerator(TemplateCompiler compiler, TemplateConfig config, Con
     @Override
     public void onImport(String importClass) {
         writePackageIfRequired();
+        imports.add(importClass);
         kotlinCode.append("import ").append(importClass).append("\n");
     }