Make a publishing script for -Nx packages

[Alexej Yaroshevich]

All for 4.x, 6.x, 7.x branches and NPM packages enb-bemxjst-4x, enb-bemxjst-6x, enb-bemxjst-7x...

What it should do:

• append -Nx to the name in package.json where N is the current major version
• prepend ~ to bem-xjst version in package.json
• execute npm publish