Add a file config + allow to specificy a terminalApp setup for linux

[wighawag]

we can now have a .newsh.json file that configure the options This is very useful as each user might have different preferences

This PR also add terminalAppSetup with is a string of argument to support terminal that do not use the usual -e <file> setup on linux

user can now specific a string like newsh --terminalAppSetup="-e {{file}}" to achieve the same