Add Halkidiki Map (#799)

## Description:
This PR adds the Halkidiki map. It's a region in Greece with rich
history that is very popular also with tourism.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

<DISCORD USERNAME>
Nikola123

resources/lang/en.json

@@ -142,7 +142,8 @@
     "deglaciatedantarctica": "Deglaciated Antarctica",
     "europeclassic": "Europe (classic)",
     "falklandislands": "Falkland Islands",
-    "baikal": "Baikal"
+    "baikal": "Baikal",
+    "halkidiki": "Halkidiki"
   },
   "map_categories": {
     "continental": "Continental",