Add metadata inheritance from parent groups and option to not inherit the metadata

[sihlecodes]

Please check if the PR fulfills these requirements:

• [x] The commit message follows our guidelines.
• For bug fixes and features:
  • [x] You tested the changes.
  • [x] You updated the docs or changelog. (Only Manual.md, I don't know what tool to use to generate the html)

Related issue (if applicable):

What kind of change does this PR introduce?

Fixes bug #49 Small UI change Introduces a new feature

Does this PR introduce a breaking change?

Not 100% sure. But all my tests went as expected.

New feature or change

Introduces a feature I call "metadata inheritance", which allows group layers that are not marked for export to share their metadata to child layers. Reduces the clutter in layer names and makes it easier to organize larger documents.

Introduced a new tag i=no|false which makes layers ignore all inherited metadata. Group Layers can still share their own defined metadata with their children when marked with i=.

What is the current behavior?

Layers have to be multi selected to change, often similar, metadata.

What is the new behavior?

A single group layer can share common metadata tags to child layers while still allowing child layers to override those tags if needed.

Other information

Fixed #49 Changed the update button on the UI to be inline with the line edit and replaced the "Update" text with the "view-refresh" icon.

[razcore-rad]

I gave it a quick look and try, it's a really nice contribution, thanks a lot.

[NathanLovato]

We need to contribute the changes to Krita as well. If you have a KDE gitlab account, could you do it @razcore-rad? All we need to do is update the addon files. Perhaps rename one or two as well, I don't remember exactly.

Here's the source repository: https://invent.kde.org/graphics/krita