Feature/partial views

[julczka]

This PR adds CRUD UI for partial views & folders.
Almost everything works against the real API except:
tree does not refresh when you remove a folder or file, I have no idea why, it's the same request that works once and is not done the other time.
There is a nasty, hacky solution in this PR to distinguish between file, folder and empty folder and display different actions. I think the conditions array in manifests you should be able to also pass a function, not only an alias - maybe a condition instead of being an array of strings should be an array of Condition interface that will have an alias and optional filetrFuction that will be run every time you should determine if the extension should show up or not? Anyway, there is an urgent need for something nicer then what I have done in here, cause what I have done is quite dumb :)

Description

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (minor updates related to the tooling or maintenance of the repository, does not impact compiled assets)

Motivation and context

How to test?

Screenshots (if appropriate)

Checklist

• If my change requires a change to the documentation, I have updated the documentation in this pull request.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.