Add Merge Tags and Delete Tags operations

[asitemade4u]

Tag operations in Linkding are limited to the bare minimum: add, search, and recently search untagged entries.

Merging tag and Deleting Tags are operations that should be included, IMO.

Currently, here are the operations required to merge two tags in Linkding:

1. detect the duplicates in the "tag cloud" on the right (not really practical)
2. select the first duplicate and sevaluate the number of linked entries
3. select the second duplicate and sevaluate the number of linked entries
4. now select the less-used tag in the couple and batch-add the other tag

That is too complex and prone to errors (personnaly, I do it using a SQLite client, but even then it is awkward).

So PLEASE:

1. add a Delete Tag operation
2. add a Merge Tags operation

[sissbruecker]

Deleting tags is possible through the admin UI.

Merging would be nice to have. In the meantime it can be worked around with the bulk operations as you described.