Allow referencing large CSV files in vocabularies

When importing very large CSV files in a Studio project, there are several problems:

• the project may not load because large vocabulary is sent (with other features) in a single request that times out (Amazon load balancer times out at 60s)
• the vocabulary editor is not usable (too many elements)

To better manage this use case, let's allow users to reference a CSV file that can be used as is at runtime.

Users may be able to reference the file from the creation page, or from the "import CSV" popup.
When given a CSV file, Studio offers to convert to "read only" mode when vocabulary has more than 100 entries (from creation page or import).
If there are any existing values in the vocabulary, they will be removed.

Once referencing a CSV file, vocabulary cannot be switched back to "editable" mode, only the CSV file can be modified and re-uploaded.

Ideally, the CSV file content should be still validated server side to spot issues with its format.