Noetic gazebo classic

[Guillaumebeuzeboc]

These are the changes to build a snap for ROS noetic compatible with the TB3 robot as well as the Gazebo classic simulation.
The main differences are:

• use of the snap daemons functionalities for map saving and others
• maps are now saved in SNAP_USER_COMMON/map (user being root in snap daemons)
• the core daemon can be enabled to run next to the Gazebo classic simulation
• the robot can be teleoperated by the keyboard or a joystick

This PR is meant to be compatible with turtlebot3c noetic-devel

This PR is a replacement for #1

[Guillaumebeuzeboc]

An idea I had. With:

+
+# enable navigation or even restart it on a new map
+snapctl start --enable turtlebot3.navigation
+

we could automatically enable and start the navigation right after saving the map. This way the snap is first installed with the navigation disabled. And as soon as you run the mapping once it automatically enables the navigation.
What do you think? is it too much?

[Guillaumebeuzeboc]

An idea I had. With:

+
+# enable navigation or even restart it on a new map
+snapctl start --enable turtlebot3.navigation
+

we could automatically enable and start the navigation right after saving the map. This way the snap is first installed with the navigation disabled. And as soon as you run the mapping once it automatically enables the navigation. What do you think? is it too much?

No need for that since it would complicate the snap for not much feature

[artivis]

I made a last small suggestion. Otherwise LGTM 👍 !