Refracted brew tasks to run from inside bash commands, thus implicitly importing the user’s default shell and its environment variables.

Removed annoying “Test” tooltip from main window.
Removed custom brew path window and disabled preferences window.

These both are no longer necessary. The current implementation runs Homebrew from an instance of the user’s default shell, thus implicitly importing all user’s default environment variables.
Therefore, if a command works on Homebrew, it should work on Cakebrew.