Error artwork (#1000)

* Add new Elephant Friend images. Use them in ListsActivity.

* Add error images to AccountListFragment

* Add error images to Timeline & Notifications fragment. Needs rework.

* Introduce BackgroundMessageView. Use it in AccountList.

* Use correct button style for BackgroundMessageView

Co-Authored-By: charlag <charlag@tutanota.com>

* Use BackgroundMessageView

* Add BackgroundMessageView docs

* Re-color and document elephants

* Apply feedback, disable refresh when error is shown

* Fix string typo

app/src/main/java/com/keylesspalace/tusky/view/BackgroundMessageView.kt

@@ -0,0 +1,46 @@
+package com.keylesspalace.tusky.view
+
+import android.content.Context
+import android.util.AttributeSet
+import android.view.Gravity
+import android.view.View
+import android.widget.LinearLayout
+import androidx.annotation.DrawableRes
+import androidx.annotation.StringRes
+import com.keylesspalace.tusky.R
+import com.keylesspalace.tusky.util.visible
+import kotlinx.android.synthetic.main.view_background_message.view.*
+
+
+/**
+ * This view is used for screens with downloadable content which may fail.
+ * Can show an image, text and button below them.
+ */
+class BackgroundMessageView @JvmOverloads constructor(
+        context: Context,
+        attrs: AttributeSet? = null,
+        defStyleAttr: Int = 0
+) : LinearLayout(context, attrs, defStyleAttr) {
+
+    init {
+        View.inflate(context, R.layout.view_background_message, this)
+        gravity = Gravity.CENTER_HORIZONTAL
+        orientation = VERTICAL
+
+        if (isInEditMode) {
+            setup(R.drawable.elephant_offline, R.string.error_network) {}
+        }
+    }
+
+    /**
+     * Setup image, message and button.
+     * If [clickListener] is `null` then the button will be hidden.
+     */
+    fun setup(@DrawableRes imageRes: Int, @StringRes messageRes: Int,
+              clickListener: ((v: View) -> Unit)?) {
+        messageTextView.setText(messageRes)
+        messageTextView.setCompoundDrawablesWithIntrinsicBounds(0, imageRes, 0, 0)
+        button.setOnClickListener(clickListener)
+        button.visible(clickListener != null)
+    }
+}