I used the following already existing packages:
robotiq for the gripper (https://github.com/ros-industrial/robotiq) (I deleted the 3 Finger packages because I don't need it) universal_robot for the ur10e robot (https://github.com/ros-industrial/universal_robot) roboticsgroup_upatras_gazebo_plugins to enable mimicked joints in gazebo (https://github.com/roboticsgroup/roboticsgroup_upatras_gazebo_plugins)
I try to move the robot and the gripper with MoveIt in Gazebo. So I combined the robot and the gripper in the "ur10e_robotiq.urdf.xacro" file in ur10e_robotiq140_moveit_config/config. I used the MoveIt setup assistant to generate the ur10e_robotiq140_moveit_config package.
The "ur10e_robotiq_conf.urdf" file is a URDF file for the simulation out of the setup assistant.