修复漫画阅读点击翻页的一些问题

新增设置某漫画阅读模式为默认值的功能
新增长按保存图片的开关

app/src/main/java/io/legato/kazusa/ui/main/explore/ExploreFragment.kt

@@ -74,7 +74,6 @@ class ExploreFragment() : VMBaseFragment<ExploreViewModel>(R.layout.fragment_exp
     private val groups = linkedSetOf<String>()
     private var exploreFlowJob: Job? = null
     private var groupsMenu: SubMenu? = null
-    private var currentSearchKey: String? = null
 
     override fun onFragmentCreated(view: View, savedInstanceState: Bundle?) {
         setSupportToolbar(binding.topBar)