Update to Alert Dialogs in api 21 and upwards.

Signed-off-by: Daniel Bailey <daniel.bailey@grappleIT.co.uk>

src/main/res/values-v21/styles.xml

@@ -29,6 +29,7 @@
         <item name="android:textColor">@color/textColor</item>
         <item name="android:textColorSecondary">@color/secondaryTextColor</item>
         <item name="colorSecondary">@color/secondaryTextColor</item>
+        <item name="android:alertDialogTheme">@style/FallbackTheming.Dialog</item>
     </style>
 
     <style name="FallbackDatePickerDialogTheme" parent="Theme.MaterialComponents.DayNight.Dialog.Alert">
@@ -47,6 +48,14 @@
         <item name="android:datePickerMode">calendar</item>
     </style>
 
+    <style name="FallbackTheming.Dialog" parent="Theme.MaterialComponents.DayNight.Dialog">
+        <item name="colorPrimary">#424242</item>
+        <item name="colorPrimaryDark">#212121</item>
+        <item name="colorAccent">#757575</item>
+        <item name="windowNoTitle">false</item>
+        <item name="android:windowBackground">@color/bg_default</item>
+    </style>
+
     <style name="Theme.ownCloud.Toolbar">
         <item name="android:windowDrawsSystemBarBackgrounds">true</item>
         <item name="windowNoTitle">true</item>

src/main/res/values/styles.xml

@@ -29,6 +29,7 @@
         <item name="colorPrimaryDark">@color/primary_dark</item>
         <item name="colorAccent">@color/color_accent</item>
         <item name="android:alertDialogTheme">@style/ownCloud.AlertDialog</item>
+        <item name="alertDialogTheme">@style/ownCloud.AlertDialog</item>
         <item name="searchViewStyle">@style/ownCloud.SearchView</item>
         <item name="android:textColor">@color/textColor</item>
         <item name="android:textColorSecondary">@color/secondaryTextColor</item>