Added couchbase-lite-core as a submodule

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "libs/couchbase-lite-core"]
+	path = libs/couchbase-lite-core
+	url = https://github.com/couchbase/couchbase-lite-core.git

android/CouchbaseLite/build.gradle

@@ -12,19 +12,35 @@ android {
         //archivesBaseName = "couchbase-lite-android"
         project.archivesBaseName = "couchbase-lite-android-${versionName}"
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
-
+        ndk {
+            abiFilters 'x86'/*, 'armeabi-v7a', 'arm64-v8a'*/
+        }
+        externalNativeBuild {
+            cmake {
+                arguments '-DANDROID_STL=c++_static', "-DANDROID_TOOLCHAIN=clang", '-DANDROID_PLATFORM=android-19', '-DJNI=TRUE'
+                cppFlags "-std=c++11 -frtti -fexceptions -fPIC"
+                // explicitly build libs
+                targets 'LiteCoreJNI'
+            }
+        }
     }
     buildTypes {
         release {
             minifyEnabled false
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
         }
     }
+    externalNativeBuild {
+        cmake {
+            path "${rootDir}/../libs/couchbase-lite-core/CMakeLists.txt"
+        }
+    }
     sourceSets {
         main {
             java.srcDirs = [
-                    "src/main/java",                      // android specific codes
-                    "${rootDir}/../shared/src/main/java" // shared java codes
+                    "src/main/java",                                  // android specific codes
+                    "${rootDir}/../shared/src/main/java",             // shared java codes
+                    "${rootDir}/../libs/couchbase-lite-core/Java/src" // lite-core java codes
             ]
         }
     }