Use a text label for UI panel buttons instead of pencil icon
- Tweaks the OO.ui.ButtonWidget settings for the Captions and Depicts panel buttons to use a text label instead of a pencil icon. The label field for each button uses the appropriate message from the internationalization files, and the progressive flag has been set in order to more closely align with the original InVision designs.
- Adds a new label in the i18n messages which should be used for both buttons; also adds the key of this message to extension.json.
Bug: T215308
Bug: T215311
Change-Id: Ibab31db5da7c12e17d362a34dd83d5eaf1965a54