Add default quickscripts

One of the features of DrRacket I am enthusiastic about is the Scripts capability.

I think it is fair to say that developers often find value in customising their tools to meet their needs.

The scripts functionality is a safe and beginner friendly way for new developers to do this without the risk of making change that negatively impacts their experience.

The list should be short - I would suggest the following would be sufficient

• Open terminal - opens the terminal in the current folder
• Get more scripts - only the script that opens the wiki page with more scripts to review and install.

The impact on the Racket installer would be minimal:

#lang racket/base
(require racket/system
         racket/path
         quickscript)

(script-help-string "Open a terminal in the directory of the current file.")

(define-script open-terminal
  #:label "Open terminal here"
  #:menu-path ("&Utils")
  #:os-types (unix macosx windows)
  (λ (str #:file f)
    (unless f
      (set! f (current-directory)))
    (define dir (path->string (path-only f)))
    (case (system-type 'os)
      [(unix)
       (system (string-append "gnome-terminal"
                              " --working-directory=\"" dir "\""
                              " -t \"" dir "\""
                              "&"))]
      [(macosx)
       (system
        (string-append "osascript -e 'tell app \"Terminal\" to do script \"cd \\\"" dir "\\\"\"'" ))]
      [(windows)
       (shell-execute #f "cmd.exe" "" dir 'sw_shownormal)])
    #false))

(define-script more-scripts
  #:label "Get more scripts (browser)"
  #:menu-path ("url2script")
  #:help-string "Opens the Racket wiki page for DrRacket Quickscript scripts."
  (λ (str) 
    (send-url "https://github.com/racket/racket/wiki/Quickscript-Scripts-for-DrRacket")
    #f))

Review the quickscript API and the DrRacket installer integration described in the issue. Verify the proposed default scripts on Unix, macOS, and Windows; done means both scripts appear in the Scripts menu, open a terminal in the current folder where supported, and open the Quickscript wiki page.