implicit selection of dialogue graph

[ThierryBerger]

Hello,

I thought the save/load process might benefit some improvements, such as being closer to the one of the "Animation" Window, so this pull request does a few tweaks to the loading/saving process.

quick changelog:

• The "Narrative graph" load the selected asset graph from project selection
• The title changes to reflect current selection to avoid doubt on which file is selected
  • this idea is from major code editors, where we could also add an asterisk * if there's modifications to be saved.
  • modifying title is not very unity-esque so I'm less sure now...
• no "Load" anymore
• "save" and "new" dialogue file process reworked to use unity file selector

[mert-dev-acc]

Hey there! Thanks for the PR! Looks good.

Although, when I test it I got some errors while creating a new narrative as follows. If you can take a look at it. That would be great 👍

ArgumentException: This visualElement is not my child
UnityEngine.UIElements.VisualElement+Hierarchy.Remove (UnityEngine.UIElements.VisualElement child) (at C:/buildslave/unity/build/Modules/UIElements/VisualElementHierarchy.cs:304)
UnityEngine.UIElements.VisualElement.Remove (UnityEngine.UIElements.VisualElement element) (at C:/buildslave/unity/build/Modules/UIElements/VisualElementHierarchy.cs:108)
Subtegral.DialogueSystem.Editor.StoryGraph.OnDisable () (at Library/PackageCache/com.subtegral.dialoguesystem@dd88cc6595be1c89f00a67dc1c0179ba695f791b/com.subtegral.dialoguesystem/Editor/Graph/StoryGraph.cs:124)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

[ThierryBerger]

I was on unity 2.9 if that’s of any help, I’ll take a look at your error when possible!

[ThierryBerger]

Well indeed this PR needs more work, after a fresh install on mac, it had problem saving narrative files.

Well, I doubt I'll do more work on this Pull Request any time soon, thanks for your time :)

[mert-dev-acc]

No worries! I'll probably edit your PR and push it when I do. Thanks for your great contribution Thierry! :)