May fail in Shiny with weird function names

[klmr]

Currently, the code checks for Shiny by walking the call stack, looking for a call to shiny::runApp.

There are two caveats:

1. As mentioned in a user group discussion, this may fail when runApp is invoked differently (which could happen).
2. Even without any change in the invocation, there may be convoluted situations where multiple functions called runApp are on the call stack. In such cases, the check will fail.