Update the Batch Exporter Python plugin

We got a contribution for batch exporter that fixes a bug and adds a new config option.

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Here's a copy-paste of the original PR from on our repo

Please check if the PR fulfills these requirements:

• The commit message follows our guidelines.
• For bug fixes and features:
  • You tested the changes.
  • 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.

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Other notes

1. I've also updated the Manual.html so all should be fine with this MR.
2. This was a previous MR that I botched by removing by mistake the license comments and there were a few other mistakes. I recreated the branch with one commit instead of trying to fix the history on the other MR.