Open photos embedded in preview cards in the image viewer (#1966)

* Open photos embedded in preview cards in the internal image viewer instead of opening the browser

* Enable toolbar for single image viewer

* Apply review feedback

app/src/main/java/com/keylesspalace/tusky/pager/SingleImagePagerAdapter.kt

@@ -0,0 +1,25 @@
+package com.keylesspalace.tusky.pager
+
+import androidx.fragment.app.Fragment
+import androidx.fragment.app.FragmentActivity
+import com.keylesspalace.tusky.ViewMediaAdapter
+import com.keylesspalace.tusky.fragment.ViewMediaFragment
+
+class SingleImagePagerAdapter(
+        activity: FragmentActivity,
+        private val imageUrl: String
+) : ViewMediaAdapter(activity) {
+
+    override fun createFragment(position: Int): Fragment {
+        return if (position == 0) {
+            ViewMediaFragment.newSingleImageInstance(imageUrl)
+        } else {
+            throw IllegalStateException()
+        }
+    }
+
+    override fun getItemCount() = 1
+
+    override fun onTransitionEnd(position: Int) {
+    }
+}