Flags: Update outdated flags (tv and tk) and add new ones

In https://github.com/jamulussoftware/jamulus/pull/2409#issuecomment-1053559073 we've added support for previously unsupported territories. This is a follow-up to update the flags:
- [ ] The newly supported `tv` and `tk` flags are historical versions which no longer match the current flag of those countries as per https://en.wikipedia.org/wiki/Country_code_top-level_domain
- [ ] All existing flags should probably be checked for necessary updates (#2409 only checked the 53 newly added flags)
- [ ] Qt support some territories which we do not have flags for. Some probably don't make sense in our usage (World, Europe), but others might be worth adding:

```
8 Antarctica
29 Bouvet Island
75 Guernsey
78 French Southern Territories
95 Heard And McDonald Islands
152 Cura Sao
196 South Georgia And The South Sandwich Islands
238 Canary Islands
241 Clipperton Island
244 Saint Barthelemy
245 Saint Martin
246 Latin America
247 Ascension Island
249 Diego Garcia
250 Ceuta And Melilla
251 Isle Of Man
252 Jersey
253 Tristan Da Cunha
254 South Sudan
255 Bonaire
256 Sint Maarten
257 Kosovo
258 European Union
259 Outlying Oceania
260 World
261 Europe
```

**Describe the solution you'd like**

The outdated flags should be replaced by newer versions.
The original author of the flags which are used in Jamulus (https://famfamfam.com) does not provide newer versions of `tk` and `tv`.

**Describe alternatives that have been considered**

Keep flags outdated, don't add new ones.

Note: I think this is a really low-prio issue for now. I'm not adding a milestone therefore.
cc @jamulussoftware/designers

Inizia esaminando le modifiche alle bandiere della pull request #2409 e confronta le immagini attuali di tv e tk con le bandiere nazionali attuali a cui si fa riferimento in Wikipedia. Poi verifica le bandiere esistenti e l’elenco dei territori di Qt per individuare le aggiunte mancanti, utilizzando gli assets di famfamfam quando disponibili. Il lavoro è completato quando le bandiere obsolete sono state sostituite e tutti i territori mancanti che vale la pena includere sono stati aggiunti o esplicitamente esclusi.

Scritto dal modello di indicizzazione a partire dal testo della issue.