Add java API and shiny control to let user load a dataset as csv file

[amattioc]

Users cannot load datasets outside of VTL code today. This creates some limitations with the VTL Studio in shinyapps because neither local csv files nor the R environment can be used in that situation (so, only SDMX datasets can be used).

To overcome this limitation, an explicit shiny control could be added to vtl studio, that allows users to upload a dataset in the csv environment. This could be a fileInput button that selects the file, and calls a java API that streams the files and puts it in the csv environment, ready to be used in vtl scripts.

[vpinna80]

Closed by 40faf9c.