#485 Enhance Lurch update mechanism to include release notes and libraries

[Nathan Carter]

1. Keep on our website a simple XML file with the latest information about our releases. An example such file has been posted at [http://lurch.sourceforge.net/releaseinfo.xml]. Write a script to regenerate the XML file and upload it, and add the running of that script to the list of things to do when releasing (a list that needs updating anyway). The library release date in the file should be the time at which the script was run.
2. Tweak the existing Lurch update mechanism so that instead of fetching [http://lurch.sourceforge.net/downloads] and scraping it for a version number, it fetches [http://lurch.sourceforge.net/releaseinfo.xml] and parses the XML. Be sure to notice all of the new data in that file as part of your parsing, beyond the simple one-floating-point value that scraping now obtains.
3. Enhance the {{{LurchVersionChecker}}} class so that when the comparison indicates that the app is out-of-date, the dialog shows not only the two version numbers, but also the new release notes in a show-details zone, because the new release notes came in the fetched XML file.
4. That dialog should also check to see if the user's libraries are out-of-date, and thus show the dialog in that case as well. The libraries should be considered out of date if an entry in the XML file for libraries matches the version number of the user's current app (so that the format could support multiple library entries for multiple Lurch versions in the future if that became important...e.g., libraries for the old Lurch 1.0 users and different ones the new Lurch 2.0 users) and yet the release date for those libraries is newer than the creation date on the user's actual library files on their hard drive.
5. If the user says they want to download the newest libraries, Lurch should use the given URL and filenames to fetch them one at a time, and place them in the user's installed libraries (overwriting existing files if need be), essentially as if someone had done {{{scp <all the="" files="" on="" web=""> User'sLurchInstallation/libraries/}}}. A progressbar will appear while that's happening and let them close the dialog when it's done. Ensure that the files installed in this way have their creation dates explicitly set by Lurch. (Or last-modified dates, if creation dates aren't possible.) [http://stackoverflow.com/questions/4963295/setlastmodified-date-with-qt]</all>