add new extension category for language packs

[chrisdias]

We need to add a new category for package.json categories. the proposal is this:

• Rename "Languages" to "Programming Languages" in the Marketplace
  • Keep the Languages category for package.json
• Add a new category to the marketplace called "Language Packs"
• Add a new category for package.json called LanguagePack

[chrisdias]

https://github.com/Microsoft/vscode/blob/d917cc6bc408822160ff2aad2f3a223c7f5d1e51/src/vs/platform/extensions/common/extensionsRegistry.ts#L151

not sure if it needs to be added anywhere else.

[sandy081]

Added Language Packs category to package.json. To be consistent with other categories, made it plural and added space.