Permission added for manual xml edition

As it can override other permissions
added an XMLRPC SSL option to configuration

Added a note that you must use a SSL proxy to do that
Add xmlrpc ssl configuration option in archipel.conf
Fix #634 - Avoid empty values in configuration file
Revert "Permission added for manual xml edition"

This reverts commit 73f2d66c1e198e7de6ef221f3048e69e1810aafe.
Merge pull request #667 from CyrilPeponnet/security-improvements

Security improvements and bug fix