[build] Move shared and gradle-plugin into separate gradle builds

Platform libs build will be changed by a separate commit

backend.native/debugger-tests/build.gradle

@@ -4,7 +4,7 @@ apply plugin: 'kotlin'
 dependencies {
     compile "org.jetbrains.kotlin:kotlin-stdlib:$buildKotlinVersion"
     compile project(path: ':backend.native', configuration: 'cli_bc')
-    compile project(':shared')
+    compile 'org.jetbrains.kotlin:kotlin-native-shared'
     compile 'junit:junit:4.12'
 }