Moved Settings to be a regular page, not a free-floating window

[andreww-msft]

Summary

Before this, PI Settings were provided in a separate free-floating window. This change moves PI Settings into the main window as a page, using the same basic navigation model as Dev Home Settings.

Details

This meant creating a new viewmodel and page for the main settings UI, and for each of the 4 sub-pages, and registering these with the navigation service and page service. Per Dev Home model, moved the various UI event handlers to command-binding with RelayCommands in the viewmodel (although I mostly left the AdditionalTools page alone after the port, because we have a backlog item to redesign this piece anyway).

Reimplemented all the Settings sub-pages to match Dev Home's model: moved custom border items to SettingsCards, SettingsExpanders and so on. Added simple breadcrumb navigation. Created PIAppInfoService, which is a subset of Dev Home's AppInfoService. Deleted the old SettingsToolWindow & ToolWindow classes, moved the AddTools and EditTools controls to the Controls folder/namespace and deleted the SettingsUi folder.

In the ExpandedView, moved the Settings button to the bottom of the left nav-list, and reworked the grid layout to ensure Settings is at the bottom regardless of whether there's a perf counter row. Deleted the SettingsNavLink class as its now redundant. Note that the main PI nav mechanism is different from Dev Home's main nav model, and we have a backlog item to update this to a NavigationView.

Here's the main Settings page in the PI expanded view:

Breadcrumbs and page navigation...

[zadesai]

[jaholme]