Add in updates for Mac build and package

[PropGit]

[EDITED] Summary of changes:

• Added package subfolder and moved root resources used for packaging (not building) into it
• Created distribution resources for Mac (in package subfolder)
• Created mac_app_sign_and_package.sh script (in package subfolder) to:
  • deeply digitally sign the BlocklyPropClient.app application bundle (in the ./dist subfolder)
  • create a signed FTDI USB Driver installer package
  • create a signed BlocklyPropClient-#.#.#-setup-MacOS.pkg installer package (in the ./dist subfolder)
  • perform a number of safety checks along the way
  • This PR marks the first time our BlocklyPropClient package is more of an installer which installs BlocklyPropClient as well as the FTDI USB drivers and requires a system restart (for the drivers to work properly).

Additional details:

• Disabled UPX (it wasn't needed anymore)
• Updated .gitignore to exclude VPython subfolder and .app and .pkg files

[PropGit]

@zfi - Before merging this, let's talk. I've found an issue that I can't explain fully right now.

• It appears the application bundle does not have a /Contents subfolder where everything else resides... instead, everything else is right at the root of the .app bundle. This may be due to a mistake in my script; unknown.
• The current builds (from this PR's tip which, of course, amends the tip of demo that includes log file generation now) installs properly, but the client app runs and immediately fails due to "Permission Denied" on writing the log file, which appears to be located within the application bundle. I'm not sure if that's the location that was intended.
• The app will run if sudo'd from the command-line

[paragitadmin]

The code to place the log file under MacOS looks for the ~/Library/Logs/Parallax/ folder. If it does not find that, it tries to create it. If it is unable to do so, it reports a failure to the init() function which, in turn, tells the main that the logger is unable to proceed with file logging.

PR #43 has been submitted to correct this issue.

[PropGit]

Thanks @zfi - That's a fantastic solution. I'll test it out this morning and try to determine why my build doesn't seem to use a Contents subfolder also; don't know why that's happening nor if it's a real problem or not at the moment.