Rename default volumes `data` and `output` in order to avoid name collisions

[averdones]

Is your feature request related to a problem? Please describe. One of the folders in the docker image that I created to use with mercure was called data.

I didn't know at first why my program was failing at finding the subfolders and files inside my data folder, until I realized that mercure had also a folder called data that was overwriting my folder.

Describe the solution you'd like Rename both data and output volumes in here as suggested by @tblock79.

@tblock79 suggested renaming them to something like mercure_data and mercure_output. I am thinking that adding an underscore in front could help even more (or something even more unique). I can see myself being silly enough to name a folder mercure_data just because I am working with mercure.

Also, the presence of this two folders and, in general, the folder structure of the docker image could be better documented somewhere.

Describe alternatives you've considered

Additional context

[RoyWiggins]

I've moved the folders into /tmp/, which should solve the issue- it would be quite unlikely for a container to include important things in /tmp.

see commit