Tags/Categories: Add support for category/tag management

[rachelmcr]

Currently, the only way to manage categories and tags in the app is to add or remove them from individual posts in the post options (in the editor). Users regularly request a way to manage (edit/delete) categories and tags outside of the editor.

Calypso currently has category/tag management in the site's General Settings: https://wordpress.com/settings/writing

You can add a new category/tag, and edit, delete, set as default, and view posts using each category or tag:

It would be nice to have similar category/tag management in the app.

Tested on iPhone 6, iOS 10.2.1, WPiOS 7.2.0.20170313.

[rachelmcr]

Example app review from a user requesting this feature:

The interface is pretty good, but the only way to edit categories/tags is to open up a post and do so from within that interface. It's not intuitive if you just want to jam away on adding/editing a bunch of categories/tags.
I want a stand-alone category/tags interface similar to the one seen in the admin panel as if I was accessing it from my browser. If the app had a categories/tags interface I would give this app 4 or 5 stars.

[kurzee]

Related: #6862

[rachelmcr]

This came up again in user feedback (Internal ref: AppbotX 28306):

There is no way i can change and rename my cathegories.

[sarahblackstock]

App review requesting more category management options:

when you make subcategories there is no way to delete them?? or change or edit any categories.

[elibud]

This has been implemented by @ctarda and is shipping on version 9.2.