Content type saving performance improvements.

[KevinJump]

v9.2 contains some more performance improvements for saving of content and content types.

• Don't save items when the internal serializer returns saved as part of the action (reduces save count in some syncing instances)
• Sort content/media by both level and sort order before importing - reduces the need for a second pass on content/media
• New option flag to not save/publish content at all if we don't think its changed after a 'full import'

OnlyPublishDirty

When you perform a full import, uSync runs through the whole import process regardless of detecting changes, this isn't really required but can be used to 'force' a sync of something if uSync isn't detecting the change (it is far more likely that uSync would detects a change that isn;'t there then there being a change in the file not detected by uSync,)

at the end of this process content will be published, even if it hasn't changed, - the "OnlyPublishDirty" flag lets you change this behaviour, and only publish content if Umbraco thinks it is dirty (so less DB/File/Cache hits).

"uSync": {
  "Sets": {
    "Default": {
      "HandlerDefaults": {
        "OnlyPublishDirty": true
      }
    }
  }
}

in 9.x this value will be false by default (so no behaviour change) if this value is usefull and has no side effects we might flip this to true for v10.