"Create new temporary project..." on Start Page disappears after undocking and redocking the Start Page

[Neme12]

Followup to #5

More details in this comment:

TemporaryProjects/TemporaryProjects.14.0/StartPageExtender.cs

Lines 77 to 88 in 7de2b12

	// If you try to make any improvements here, please make sure not only that the button is visible
	// when the start page is opened, but also:
	// 1. When the user switches to another tab and back to the start page
	// 2. When the start page is undocked by dragging the tab
	// 3. When the start page is docked again (this currently *doesn't* work)
	// 4. The button is never duplicated, for example when switching focus to a different tool window and back
	// I've tried many approaches such as doing this in OnFrameIsVisibleChanged, OnActiveFrameChanged,
	// IVsWindowFrameNotify.OnShow using IVsWindowFrame2.Advise and even DTE.Events.WindowEvents.
	// With all of these approaches there are cases where the button is not recreated because the event is not fired,
	// and in some cases it's even fired twice. The current solution is a compromise - the common case works and
	// undocking the start page is presumably not that common.