During app teardown, the Application object may be destroyed before
something else, and so having Application::the() return a reference was
obscuring the truth about its lifetime.
This patch makes the API more honest by returning a pointer. While
this makes call sites look a bit more sketchy, do note that the global
Application pointer only becomes null during app teardown.
We now show a list of running processes that the user can choose from.
After choosing one, we start profiling it and show a timer with a stop
button that the user has to press to stop profiling.
