Update to android_core 0.4.0

[jubeira]

This is required for https://github.com/rosjava/android_apps/pull/80 to work properly; otherwise the dependency chain breaks:

• android_apps 0.4 --> android_core 0.4 and
• android_apps 0.4 --> android_remocons 0.2 --> android_core 0.3.

If android_remocons still use the old android_core, android_apps cannot be compiled. With this change, android_remocons also will also depend on android_core 0.4

[jubeira]

@ernestmc Same as https://github.com/rosjava/android_core/pull/286#issuecomment-427120931; to build this before merging android_core, replace the buildscript block in the top level Gradle script with this:

// Replace external buildscript with this:
buildscript {
  apply from: "https://github.com/jubeira/rosjava_bootstrap/raw/task/add_google_repo/buildscript.gradle"
  dependencies {
    classpath "com.android.tools.build:gradle:3.2.0"
  }
}

apply plugin: 'catkin'

// Add the repositories block here
allprojects {
  group 'com.github.rosjava.android_remocons'
  version = project.catkin.pkg.version
  repositories {
    google()
    jcenter()
  }
}

After merging the PR in android_core this one should build without that hack.