Fix MangaSource import and improve user agent handling

MangaSource class was imported twice from different packages.

app/src/main/kotlin/org/koitharu/kotatsu/browser/BrowserActivity.kt

@@ -22,7 +22,6 @@ import org.koitharu.kotatsu.core.ui.BaseActivity
 import org.koitharu.kotatsu.core.util.ext.configureForParser
 import org.koitharu.kotatsu.core.util.ext.toUriOrNull
 import org.koitharu.kotatsu.databinding.ActivityBrowserBinding
-import org.koitharu.kotatsu.parsers.model.MangaSource
 import javax.inject.Inject
 import com.google.android.material.R as materialR
 
@@ -45,7 +44,7 @@ class BrowserActivity : BaseActivity<ActivityBrowserBinding>(), BrowserCallback
         }
         val mangaSource = MangaSource(intent?.getStringExtra(EXTRA_SOURCE))
         val repository = mangaRepositoryFactory.create(mangaSource) as? ParserMangaRepository
-		repository?.getRequestHeaders()?.get(CommonHeaders.USER_AGENT)
+        val userAgent = repository?.getRequestHeaders()?.get(CommonHeaders.USER_AGENT)
         viewBinding.webView.configureForParser(userAgent)
         CookieManager.getInstance().setAcceptThirdPartyCookies(viewBinding.webView, true)
         viewBinding.webView.webViewClient = BrowserClient(this)