Added menu GUI!

Based on menu and winDialog.
Updated functions:

   * ask.user.yn.question - added a menu based GUI.
   * check.for.updates.R - added a menu based GUI.
Ask the user if to install R or not - When using the menu system.
Added installr function

A function to allow users to choose which software to install.
Also added it to the menusystem.
Changes install.Rtools defaults