About page (#78)

* added about page with version info
* lock drawer to closed state for About screen. Added About screen hardware back button handling.

src/main/java/io/lbry/browser/reactmodules/VersionInfoModule.java

@@ -0,0 +1,38 @@
+package io.lbry.browser.reactmodules;
+
+import android.content.Context;
+
+import com.facebook.react.bridge.Promise;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.ReactMethod;
+
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+
+public class VersionInfoModule extends ReactContextBaseJavaModule {
+    private Context context;
+
+    public VersionInfoModule(ReactApplicationContext reactContext) {
+        super(reactContext);
+        this.context = reactContext;
+    }
+
+    @Override
+    public String getName() {
+        return "VersionInfo";
+    }
+
+    @ReactMethod
+    public void getAppVersion(final Promise promise) {
+        PackageManager packageManager = this.context.getPackageManager();
+        String packageName = this.context.getPackageName();
+        try {
+            PackageInfo packageInfo = packageManager.getPackageInfo(packageName, 0);
+            promise.resolve(packageInfo.versionName);
+        } catch (PackageManager.NameNotFoundException e) {
+            // normally shouldn't happen
+            promise.resolve("Unknown");
+        }
+    }
+}