add About and License activities

app/src/main/java/com/simplemobiletools/filemanager/activities/LicenseActivity.java

@@ -0,0 +1,32 @@
+package com.simplemobiletools.filemanager.activities;
+
+import android.content.Intent;
+import android.net.Uri;
+import android.os.Bundle;
+import android.support.v7.app.AppCompatActivity;
+
+import com.simplemobiletools.filemanager.R;
+
+import butterknife.ButterKnife;
+import butterknife.OnClick;
+
+public class LicenseActivity extends AppCompatActivity {
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_license);
+        ButterKnife.bind(this);
+    }
+
+    @OnClick(R.id.license_butterknife_title)
+    public void butterKnifeClicked() {
+        openUrl(R.string.butterknife_url);
+    }
+
+    private void openUrl(int id) {
+        final String url = getResources().getString(id);
+        final Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
+        startActivity(browserIntent);
+    }
+}