Merge pull request #128 from ahmedcharles/settings

Fix more crashes when the window is closed before the settings dialog.
Add new clang-format for new code.
Add PackageModel and tests.

It currently doesn't do anything and doesn't even depend on package.
Have PackageModel inherit from QAbstractItemModel.

This includes stubs for all of the required functions with safe,
implementations which do nothing.
Add PackageModel manual test app.
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