Character counts on text fields

[jklewa]

The lengths of a text field (title, summary, description) can be limited by the publishing platform. Each platform determines its (often different) character limits. It would be helpful to show the current character count of these fields as well as any relevant limits imposed by the platforms, so users can know when to rephrase/truncate their text to suit the platform(s).

During edit mode, dynamically update these counts as the user types into the input fields.

This is most important for the title and summary fields, but I'm assuming description is also limited to something relatively long.