GetConfigFiles function can be used to generate a list of files, merged
from both the main configuration directory and the local configuration
directory. The local configuration directory is also able to suppress
files from the main configuration if necessary.
* Detects saving local configuration using :w and warns about
signatures.
* SaveAndSign command that will sign the file if it is a local
configuration file (other files will be unaffected)
* SignConfig command re-signs the active local configuration
