NavigationView: Adding boolean property NavigationView.IsTitleBarAutoPaddingEnabled

[RBrid]

Incremental work done for Issue #47.

We are adding a NavigationView.IsTitleBarAutoPaddingEnabled boolean property set to True by default.
When set to False, we skip adding the top padding that has the height of the title bar.

As part of these changes I also fixed the following:

• In OnApplyTemplate, the section "// Register for changes in title bar layout" was misplaced as the m_topNavGrid field was not set yet.
• NavigationView::UpdateTitleBarPadding, m_togglePaneTopPadding.Height / m_contentPaneTopPadding.Height were not reset to 0 when needsTopPadding is False.

Updated a couple of tests using the new property.