Reworked joint build (kotlin + kotlin-ultimate)

- Root buildscript classpath no more depends on buildSrc.jar from kotlin-ultimate. This allows to have stable joint builds - w/o occasional "Unresolved reference" errors in buildscripts.
- kotlin-ultimate modules are now included into Kotlin project when two conditions are met: 1) Gradle parameter 'cidrPluginsEnabled' is turned on; 2) kotlin-ultimate Git repo is checked out right to the Kotlin project root (assuming there is 'kotlin-ultimate' directory inside the project root).

buildSrc/gradle.properties

@@ -4,3 +4,5 @@ cacheRedirectorEnabled=true
 
 #buildSrc.kotlin.repo=https://jcenter.bintray.com
 #buildSrc.kotlin.version=1.1.50
+
+#cidrPluginsEnabled=true

buildSrc/settings.gradle

@@ -1,4 +1,3 @@
-
 pluginManagement {
     repositories {
         if (cacheRedirectorEnabled == 'true') {
@@ -12,3 +11,9 @@ pluginManagement {
 }
 
 include "prepare-deps"
+
+def includeCidrPlugins = hasProperty("cidrPluginsEnabled") && Boolean.parseBoolean(cidrPluginsEnabled) && file("../kotlin-ultimate").exists()
+if (includeCidrPlugins) {
+    include ":prepare-deps:kotlin-native-platform-deps"
+    project(":prepare-deps:kotlin-native-platform-deps").projectDir = file("../kotlin-ultimate/buildSrc/prepare-deps/kotlin-native-platform-deps")
+}