Rework `NoteTag`-related functionality

[igamigo]

What should be done?

We should rework the client functions for adding and removing NoteTags to the store. Currently, there are only ways to add tags (with Client::add_tag()), but they take u64s. Furthermore, these store tags are not taken into account when syncing with the node (which only uses tags for all tracked client accounts).

How should it be done?

Client and store functions should take and return NoteTag, and the client should utilize tags for syncs.

When is this task done?

• Change function signatures to store (and retrieve) NoteTag instead of u64. In terms of the SQLite store, storing u32 should be fine as it's the current format for tags.
• Utilize store tags on Client::sync_state() as well as account tags.
• Add a function for removing tracked tags.

Additional context

No response

[mFragaBA]

closing this as #266 got merged