dist.gant is supposed to be used for building IDEA Community edition only, so it's better to rename it to avoid confusion.

Previously output directory was set to '$home/out' by default, but this directory is used as the project compiler output in idea-community project, so calling dist.gant from idea-community project cleared the compiled classes.

- add dependencies module
- download and unpack JBSDK
- download and unpack Java 1.6
- download and unpack Kotlin
- download and unpack JetSign
- download JBREX and creating JBRE
- use Gradle dependencies while building IDE and while developer's
  updating

Allows storing product properties files outside of tools/idea.

download_kotlin scripts rewritten: do nothing if compatible Kotlin plugin already exists, reuse Kotlin plugin from work IDEA copy when updating from sources

move product specific properties out of build script to allow reusing build script for Android Studio

(https://github.com/JetBrains/intellij-community/pull/131 manually merged and improved)