message: Update colour picker buttons with round edges.
  ![RoundedButtons](https://user-images.githubusercontent.com/41475767/90323225-39e96500-df56-11ea-9219-d386f74fc1b4.png)
  ## Validation Steps Performed
  Deployed locally and verified that the colour picker's button has round edges.
  Closes
diff: </StackPanel.Resources>
  <Button Padding="5"
  Click="ClearColorButton_Click"
  - x:Name="ClearColorButton" x:Uid="TabColorClearButton" Content="Reset">
  + x:Name="ClearColorButton" x:Uid="TabColorClearButton" CornerRadius="2" Content="Reset">
  </Button>
  <Button Padding="5"
  Click="ShowColorPickerButton_Click"
  - x:Name="CustomColorButton" x:Uid="TabColorCustomButton" Content="Custom...">
  + x:Name="CustomColorButton" x:Uid="TabColorCustomButton" CornerRadius="2" Content="Custom...">
  </Button>
  </StackPanel>
  </StackPanel>
  