gradle: update to 2.1 and android targetSdk 21

- add android-appcompat subproject

vtm-desktop/build.gradle

@@ -20,9 +20,11 @@ mainClassName = 'org.oscim.gdx.GdxMapApp'
 //}
 
 sourceSets {
-  main.java.srcDirs = ['src']
-  //main.resources.srcDirs = ["${buildDir}/assets"]
-  output.resourcesDir = 'assets'
+  main {
+    java.srcDirs = ['src']
+    //main.resources.srcDirs = ["${buildDir}/assets"]
+    output.resourcesDir = 'assets'
+  }
 }
 
 dependencies {
@@ -31,7 +33,7 @@ dependencies {
   //compile "com.badlogicgames.gdx:gdx-backend-lwjgl:$gdxVersion"
   compile "com.badlogicgames.gdx:gdx-backend-jglfw:$gdxVersion"
   compile "com.badlogicgames.gdx:gdx-platform:$gdxVersion:natives-desktop"
-  compile 'org.slf4j:slf4j-simple:1.7.5'
+  compile 'org.slf4j:slf4j-simple:1.7.6'
   compile files('../vtm-ext-libs/gdx/vtm-jni-natives.jar')
 }