Remove dependency injection from core module and data module from presentation-widget module

Includes side effects:
- No longer need to restart app for user agent string change to take effect
- parseAs extension function requires a Json instance in the calling context, which doesn't necessarily need to be the default one provided by Injekt

app/src/main/java/eu/kanade/tachiyomi/AppModule.kt

@@ -118,7 +118,7 @@ class AppModule(val app: Application) : InjektModule {
         addSingletonFactory { ChapterCache(app) }
         addSingletonFactory { CoverCache(app) }
 
-        addSingletonFactory { NetworkHelper(app) }
+        addSingletonFactory { NetworkHelper(app, get()) }
         addSingletonFactory { JavaScriptEngine(app) }
 
         addSingletonFactory { SourceManager(app, get(), get()) }