React example

[MatthijsBurgh]

superseeds #587

[MatthijsBurgh]

@snorresovold things I changed, which are good to take into account for future examples:

• Use geometry_msgs/Pose2D instead of a custom msg
• Be consistent with linting
• Remove all unnecessary dependencies, code, file, etc.

[MatthijsBurgh]

Preferably examples are tested in CI. But that requires to install and build it before it can be tested. Therefore not doing it.