Refactor mac installer (built on #2571)

[rvagg]

I've spent some more quality time with Packages today, trying to wrangle this into something closer to ready. Building on the work of @remixz work in #776 and @fhemberger's work in #2571.

• Remove the uninstall option - while I got it to work nicely and cleaned up the script to fully remove everything, the installer that Packages makes is not really suitable for an uninstall option, it still says it's "installing", the button is "install", the summary at the end still says it's installed Node & npm, it's basically a hack to make an uninstaller possible. We should consider putting this option on the wiki or even installing it somewhere in /usr/local/ that's not in PATH but we can point users to so they can run it themselves.
• Switched to the new logo using the commit on master already
• Made the "Install Node.js" option mandatory, Packages has some depend-on functionality for selecting options but there is no way to make it so you have to have Node.js if you select npm, you can make the select box turn on but you can turn it off.
• Changed install.py to add new NODE_INSTALL_NODE_ONLY, NODE_INSTALL_NPM_ONLY and NODE_INSTALL_HEADERS_ONLY (was HEADERS_ONLY) env vars so it can install npm to a different location to node so that the options work properly and you can actually opt to not install npm (yes, it works now!).
• Made it so you have to click "Customize" to get to the checkboxes to optionally install npm.
• Made the LICENSE an RTF, it looks so so much nicer now that it's formatted.
• Moved the .pkg to the top-level instead of out/, which is what the current installer does and what Jenkins expects.

Commits are all over the place and need to be compacted obviously.

Will post a test build soon, got to sort out the slaves again.

[Fishrock123]

no ?=?

[Fishrock123]

As a note, I got a few whitespace errors when applying.

[rvagg]

OK, some more adjustments and I've put Packages on both OSX build machines now (was only on one before). Now I have a test package to share! Grab it at https://nodejs.org/download/test/v6.0.0-test20160316798c9dc5b3/node-v6.0.0-test20160316798c9dc5b3.pkg to experience the new goodness.

[eljefedelrodeodeljefe]

Looks reasonable to me. Build worked like a charm. thanks @fhemberger for pointing at this one (have missed it)

[jasnell]

ping @rvagg

[jasnell]

Closing due to lack of forward progress on this.