Localize RCP app

We already added intro page to RCP app. Now we localize RCP app.

1. Let's add language-specific product definitions to "build.gradle":

products {
  product platform: 'linux', arch: 'x86_32'
  product platform: 'linux', arch: 'x86_32', language: 'de'
  product platform: 'linux', arch: 'x86_64'
  product platform: 'linux', arch: 'x86_64', language: 'de'
  product platform: 'windows', arch: 'x86_32'
  product platform: 'windows', arch: 'x86_32', language: 'de'
  product platform: 'windows', arch: 'x86_64'
  product platform: 'windows', arch: 'x86_64', language: 'de'
  archiveProducts = true
}

Here we define 8 products: 4 are English, 4 are German.