android: add missing gradle-wrapper.jar

It is required to execute the script

./gradlew tasks

The wrapper downloads the gradle version if not installed

Change-Id: I3d52f779aa6931bc4e3d57309558fdccbe98024b
Reviewed-on: https://gerrit.libreoffice.org/c/online/+/92095
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Henry Castro <hcastro@collabora.com>

android/.gitignore

@@ -1,7 +1,6 @@
 .gradle
 .idea
 /android.iml
-/gradle
 /local.properties
 /lib/src/main/assets/etc/
 /lib/src/main/assets/example.odt

android/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Fri Apr 10 17:38:50 BOT 2020
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.1.1-all.zip