convert top level classes to kotlin (#6368)

* Converted welcome activity / pager to kotlin

* Removed unused interface

* Convert ViewPagerAdapter to kotlin and enforce that all tabs must have a title that comes from strings.xml

* Convert OkHttpConnectionFactory and remove an exception class nobody was using

* Convert MapController to kotlin along with fixing nullability in a few places

app/src/main/java/fr/free/nrw/commons/WelcomeActivity.kt

@@ -0,0 +1,78 @@
+package fr.free.nrw.commons
+
+import android.app.AlertDialog
+import android.content.Context
+import android.content.Intent
+import android.os.Bundle
+import android.view.View
+import fr.free.nrw.commons.databinding.ActivityWelcomeBinding
+import fr.free.nrw.commons.databinding.PopupForCopyrightBinding
+import fr.free.nrw.commons.quiz.QuizActivity
+import fr.free.nrw.commons.theme.BaseActivity
+import fr.free.nrw.commons.utils.ConfigUtils.isBetaFlavour
+
+class WelcomeActivity : BaseActivity() {
+    private var binding: ActivityWelcomeBinding? = null
+    private var isQuiz = false
+
+    /**
+     * Initialises exiting fields and dependencies
+     *
+     * @param savedInstanceState WelcomeActivity bundled data
+     */
+    public override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        binding = ActivityWelcomeBinding.inflate(layoutInflater)
+        setContentView(binding!!.root)
+
+        isQuiz = intent?.extras?.getBoolean("isQuiz", false) ?: false
+
+        // Enable skip button if beta flavor
+        if (isBetaFlavour) {
+            binding!!.finishTutorialButton.visibility = View.VISIBLE
+
+            val copyrightBinding = PopupForCopyrightBinding.inflate(layoutInflater)
+
+            val dialog = AlertDialog.Builder(this)
+                .setView(copyrightBinding.root)
+                .setCancelable(false)
+                .create()
+            dialog.show()
+
+            copyrightBinding.buttonOk.setOnClickListener { v: View? -> dialog.dismiss() }
+        }
+
+        val adapter = WelcomePagerAdapter()
+        binding!!.welcomePager.adapter = adapter
+        binding!!.welcomePagerIndicator.setViewPager(binding!!.welcomePager)
+        binding!!.finishTutorialButton.setOnClickListener { v: View? -> finishTutorial() }
+    }
+
+    public override fun onDestroy() {
+        if (isQuiz) {
+            startActivity(Intent(this, QuizActivity::class.java))
+        }
+        super.onDestroy()
+    }
+
+    override fun onBackPressed() {
+        if (binding!!.welcomePager.currentItem != 0) {
+            binding!!.welcomePager.setCurrentItem(binding!!.welcomePager.currentItem - 1, true)
+        } else {
+            if (defaultKvStore.getBoolean("firstrun", true)) {
+                finishAffinity()
+            } else {
+                super.onBackPressed()
+            }
+        }
+    }
+
+    fun finishTutorial() {
+        defaultKvStore.putBoolean("firstrun", false)
+        finish()
+    }
+}
+
+fun Context.startWelcome() {
+    startActivity(Intent(this, WelcomeActivity::class.java))
+}