Add 'support' for additional file types in a sketch

[lmihalkovic]

I noticed that Arduino Create will support storing some sort of a README as well as a one or more images describing the sketch. I would be nice for the IDE to provide the same level of support for them.

In my case this extends to allowing some of these in libraries as well.

[lmihalkovic]

Adding support for layout details if they are present in a sketch (i.e. any images in lib or sketch can be displayed inside the editor)

[LMDONE]

[ffissore]

This has been internally discussed and there are no plans to add such features to the Arduino IDE