User management

Implement more advanced user management in the administration UI.

- [x] Split out admin functionality in separate widgets and translated them
- [x] Bring in CSV import from Nico's branch and finish off details
- [x] Add in create new user functionality
- [x] Add new `User management` navigation item that shows a list of users in the current tenant
- [x] When a user in the list is clicked it needs to bring up the manageuser widget that allows editing the user's profile information, password and privileges
- [x] Improve look and feel of the admin UI on all screen sizes
- [x] Add script to move i18n keys from widget bundles to global bundles
    - `node ./tools/crowdin/moveKeysToGlobal.js -w <Widget root dir> -k <i18n key>`
- [x] Add script to movie i18n keys from global bundles to widget bundles
    - `node ./tools/crowdin/moveKeysToWidget.js -w <Widget root dir> -k <i18n key>`
- [x] Add script to delete i18n keys from widget bundles
    - `node ./tools/crowdin/deleteKeysFromWidget.js -w <Widget root dir> -k <i18n key>`
- [x] Add script to delete i18n keys from global bundles
    - `node ./tools/crowdin/deleteKeysFromGlobal.js -r <Project root dir> -k <i18n key>`
- [x] Add new `User management` navigation item in the global admin panel as well that shows the users in the tenant
- [x] Add new `Maintenance` navigation item in the global admin panel
- [x] Add the ability to create a new global administrator (sort of, initial implementation, you can create a new user on the global administration tenant and then afterwards promote it to global admin by going into the settings for the user)
- [x] Regenerate previews
    - Reprocess specific mime types
    - Reprocess failed content previews
    - Reprocess everything in date range
    - Reprocess for a specific user
    - Reprocess all items of specific content type
- [x] Reindex search

This is a work in progress and is not ready to be merged yet. This is also depending on the work in https://github.com/oaeproject/Hilary/issues/814.