Added ItemDiscover, ItemCancel, and ScmTag permissions to the enum

These additional permissions should be useful for other standard permissions.
Reorder enums to reflect ordering in the Jenkins GUI

This is more of a readability enhancement which could potentially be useful in the event that other permissions are added to Jenkins in the future.
Merge pull request #97 from justinharringa/patch-1

Added ItemDiscover, ItemCancel, and ScmTag permissions to the Permissions enum