[RN] Add color scheme support to dialog buttons

react/features/base/color-scheme/defaultScheme.js

     'Dialog': {
         background: ColorPalette.blackBlue,
         border: getRGBAFormat(ColorPalette.white, 0.2),
+        buttonBackground: ColorPalette.blue,
+        buttonLabel: ColorPalette.white,
         icon: ColorPalette.white,
         text: ColorPalette.white
     },

react/features/base/dialog/components/native/BaseSubmitDialog.js

                         disabled = { this.props.okDisabled }
                         onPress = { this._onSubmit }
                         style = { [
-                            brandedDialog.button,
+                            _dialogStyles.button,
                             additionalButtons
                                 ? null : brandedDialog.buttonFarLeft,
                             brandedDialog.buttonFarRight
                         ] }>
-                        <Text style = { _dialogStyles.text }>
+                        <Text style = { _dialogStyles.buttonLabel }>
                             { t(this._getSubmitButtonKey()) }
                         </Text>
                     </TouchableOpacity>

react/features/base/dialog/components/native/ConfirmDialog.js

             <TouchableOpacity
                 onPress = { this._onCancel }
                 style = { [
-                    brandedDialog.button,
+                    _dialogStyles.button,
                     brandedDialog.buttonFarLeft,
                     _dialogStyles.buttonSeparator
                 ] }>
-                <Text style = { _dialogStyles.text }>
+                <Text style = { _dialogStyles.buttonLabel }>
                     { t(cancelKey || 'dialog.confirmNo') }
                 </Text>
             </TouchableOpacity>

react/features/base/dialog/components/native/InputDialog.js

                         disabled = { okDisabled }
                         onPress = { this._onSubmitValue }
                         style = { [
-                            brandedDialog.button,
+                            _dialogStyles.button,
                             brandedDialog.buttonFarLeft,
                             brandedDialog.buttonFarRight
                         ] }>
-                        <Text style = { _dialogStyles.text }>
+                        <Text style = { _dialogStyles.buttonLabel }>
                             { t('dialog.Ok') }
                         </Text>
                     </TouchableOpacity>

react/features/base/dialog/components/native/styles.js

         fontWeight: 'bold'
     },
 
-    button: {
-        backgroundColor: ColorPalette.blue,
-        flex: 1,
-        padding: BoxModel.padding * 1.5
-    },
-
     buttonFarLeft: {
         borderBottomLeftRadius: BORDER_RADIUS
     },
  * Color schemed styles for all the component based on the abstract dialog.
  */
 ColorSchemeRegistry.register('Dialog', {
+    button: {
+        backgroundColor: schemeColor('buttonBackground'),
+        flex: 1,
+        padding: BoxModel.padding * 1.5
+    },
+
     /**
      * Separator line for the buttons in a dialog.
      */
         borderRightWidth: 1
     },
 
+    buttonLabel: {
+        color: schemeColor('buttonLabel'),
+        fontSize: MD_FONT_SIZE,
+        textAlign: 'center'
+    },
+
     /**
      * Style of the close icon on a dialog.
      */