Adds an option to disable the Commit & Push button on the Commit Dialog

Using a branching model that utilizes Task/Feature Branches, where it is not desired that the entire task branch ever be pushed, the Commit dialog's Commit & Push button is dangerously close to the Commit button. 

To support that environment and prevent accidental pushes when only a Commit was desired, I've added a setting on the Get Extensions Behavior settings page to disable the Commit & Push button, along with corresponding code to disable it when the option is selected.