Tags editing and bulk operations

It must be possible to edit tags, i.e. rename or delete them.

Renaming a tag from _A_ to _B_ walks through all resources labeled with _A_, removes _A_ from them and sets _B_ instead. Deletion of a tag _X_ just removes it from all resources labeled with _X_.

Start by locating the tag-editing and resource-management entry points in the Android app, then trace how resources are labeled. The work is done when renaming a tag transfers its label from every affected resource to the new name and deleting a tag removes it from every affected resource.

Written by the indexing model from the issue text.