Add possibility to set options with the launch_elaborator() funtion call

[TammoReinders]

Enable a function call like:
launch_elaborator( file_format="rdata", file="elaborator.rdata", selected_visits=c("BL", "Visit 4", "Visit 12"))

[SHorschBay]

Many options are incorporated now in the attached branch.

Missing options are for example:

• option for ordering lab parameters
• boxplot colors
• choice of visits, treatments and lab parameters