Automatically generate "Packages" block for "Creating platform" page

[ivankravets]

We have predefined list with all available PlatformIO based packages. There is the only one place where packages are hardcoded manually. See it https://github.com/platformio/platformio/raw/develop/docs/platforms/creating_platform.rst

Need to find positions of occurrence .. _platform_creating_packages: and .. _platform_creating_manifest_file: in the contents of files and replace text which are located between them with auto-pregenerated "Packages" in https://github.com/platformio/platformio/blob/develop/scripts/docspregen.py

P.S: I propose to omit Alias column.