Fix typo in Layout Model Properties dialog.

Here’s how to replicate the typo:

1. In a display window, click Tools>Layout Model Editor.

2. Click and drag to select the components of the current layout model.

3. Go to Edit>Set properties on selected.

The dialog title should contain "Serlected" rather than "Selected".
Merge pull request #78 from jon4than/layout-model-prop-typo

Fix typo in Layout Model Properties dialog.