Installer improvements

[cwillisf]

Mac:

• Turn off BundleIsRelocatable so that the application always installs to the same place. This disables an often unexpected "feature" of PKG installers which causes the installer to search for any matching application anywhere on the target machine and install over that existing copy. This also means that a "newer" 1.1.x version will install over an "older" 1.2018xx.xx version.
• Make minimum macOS version number consistent at 10.10 -- there was one place where it was accidentally set to 10.13.
• Tweak the Makefile to clean up the dist/ directory a bit so it's easier to tell what's intermediate and what's output.
• Remove requirements.plist file which wasn't actually being used by the build process.

Windows:

• It turns out that the APIs Scratch Link uses for BLE don't work correctly in Windows 10 build 14393, so this change sets the minimum (not just "recommended") to 15063. We might be able to get 14393 working with some extra effort but I recommend seeing if there's enough demand first. I suspect this is the cause of LLK/scratch-vm#1681.
• Enforce minimum Windows build number in the installer.

I think this is the closest I can come to resolving #89 without significantly more time investment.

[cwillisf]

Test builds available here: https://www.dropbox.com/sh/e7io6584a89k65k/AAAi0jOSIUcm-RbD_JRgn3SUa?dl=0

File	Description
ScratchLinkAPPX_1.1.9.0_AnyCPU_bundle.appxupload	Microsoft Store package
ScratchLinkSetup-1.1.9.0.zip	Windows MSI installer (non-Store)
mas-scratch-link-1.1.9.pkg	Mac App Store PKG
scratch-link-1.1.9.pkg	Mac non-Store PKG

CC @BryceLTaylor

[thisandagain]

LGTM!

[evhan55]

I downloaded and ran the installer without worrying about my previous versions, and it worked well! After install, I searched for and ran "Scratch Link" via Spotlight and it correctly ran version:

Scratch Link 1.1.9 cf3c7a4
macOS Version 10.14.1 (Build 18B75)