checks that the specified folder data contains valid data in all its
  files
 
  INPUT
 
      folder_data:   - a folder containing datas formatted acording to the
                       Dynamo convention
                         OR
                       The name of a project
 
      mask:          to restict check to interior of a mask
 
      nfig:           where to plot
 
 
  OUTPUT
 
   Graphical output: a plot with the mean, max and min values of all the detected particles
 
   SYNTAX
 
   dynamo_data_check(folder_data)