Footer comments

[ljacqu]

Footer comments were added in one of the forks: SkinsRestorer/ConfigMe@8281744#diff-3ffbfe7dc32739c0f967addeb0cc4cad2edb3bbe196d94d14f43439a08ce6e1f
We can easily add this to ConfigMe.

To do

• Extend CommentsConfiguration to be able to store footer comments
  • See note below for an idea so that a separate List isn't required everywhere
• Extend ConfigurationData(Impl) to hold footer comments
• Add support for footer comments in YamlFileResource (hint: Node#endComments)
• Add unit tests
  • Ensure that footer comments are added for a normal configuration file with multiple properties
  • Ensure that footer comments are added for a config that has only one property at root path ("")

Notes

• So that it's not needed to have a separate List just for the footer comments everywhere, one idea is to add a String constant (maybe in ConfigurationData, or CommentsConfiguration?) with a dummy string that is unlikely to be a property path, and to use that as key for footers. For example, ..FOOTER is not a valid path and is guaranteed not to coïncide with a property path. Add a default method addFooterComments to CommentsConfiguration so that a user doesn't need to know about the constant.
• Introduce also a method addHeaderComments that registers them to the root path ("") for ease of us

[ljacqu]

Interesting test: if there's only one optional property, are header/footer comments added if the property is empty? Property with root path ("") or something else