external libs refactoring

. new package to keep external libs
. added script by Giampaolo Rodola'
find pset, list networks' stations

. find pset file in a given directory
. list all networks stations IDs
. minor bug fix at save_output
ui to show and warn about free space requirements, other adjustments

. widget sizing
. refactored variable name
. added detection method 'Network deviation'
. shows necessary free space
. shows available space on selected drive
. warns if necessary > available
. function to find stations ids about to be processed
function to read grid specifications file (refactored)