VOL-71: Don't declare "register to volunteer" permission in permissions-challenged Joomla sites.
VOL-71: Added permissions class to centralize permissions declarations and to override perms check function. Moved perms check from XML to preprocess function for volunteer sign-up form.
VOL-71: Get CiviCRM version from config object. Replace custom function with PHP core function version_compare(), which should work provided version numbers continue to be "PHP-standardized."
VOL-71: Updated README and in-app doc. In-app doc related to the "register to volunteer" permission appears conditionally based on the user framework.
VOL-71: Made additional changes to menu XML to enable access control in the volunteer signup form's preprocessor.
VOL-71: Replaced clunky version-checking with a real-time lookup of the user framework's support for module permissions.
Merge pull request #202 from GinkgoFJG/4.5-1.3-VOL-71

Merge changes for VOL-71 into the 4.5-1.3.x branch.