Basic live feedback functionality. Not perfect. The last call is never made. Committing to be able to build release version on master.
Merge branch 'master' into async-thread-callback
Fixed issues #38, #18 and #14.

Now adds user $PATH to Cakebrew’s environment variables before running.
Doctor and Update now run on separate threads with live feedback to the user, just like in terminal.
Added clear button to update task. Fixed bug in which sidebar selection would vanish.