Raise an error during capture if CutyCapt is not installed

If CutyCapt is not installed and I attempt to capture a webpage, the current error is cryptic:

    sh: --: invalid option
    Usage:  sh [GNU long option] [option] ...
      sh [GNU long option] [option] script-file ...
    GNU long options:
      --debug
      --debugger
      --dump-po-strings
      --dump-strings
      --help
      --init-file
      --login
      --noediting
      --noprofile
      --norc
      --posix
      --protected
      --rcfile
      --restricted
      --verbose
      --version
      --wordexp
    Shell options:
      -irsD or -c command or -O shopt_option    (invocation only)
      -abefhkmnptuvxBCHP or -o option

I added a friendly error message instead:

     RuntimeError: Cutycapt is not installed.