Separate data and metadata editing logic

[roll]

Overview

Initially, Open Data Editor was meant to be an IDE so it made sense to have panel based Metadata editor with an ability to simultaneously see and edit the data and metadata. As of now it is more of a simple tabular data validator, there is no reason to keep this complexity.

Currently, the most problematic parts are:

• patch logic on the server where there are endpoints that expect both data and metadata updates in the same call
• some client logic in the store that is overcomplicated because it needs to keep track of both data and metadata editing state

The simplest solution would be to rebase metadata editing on a dialog with separate "Save/Close" logic and keep only data editing in the main mode.