Fixes for handling of oversized map dwellings

- Marked large version of H3 Unicorn's Glade as not usable for random
dwelling replacement
- Shifted oversized dwellings - that have at most 2x2 as blocked tile,
but have non-blocked tile column will now be placed correctly
- This fixes incorrect random dwelling replacement of the only oversized
H3 dwelling - Portal of Glory
- Game will now detect & report invalid dwelling templates from mods
- Updated docs to clarify dwellings format

docs/modders/Map_Objects/Dwelling.md

@@ -9,6 +9,11 @@
 		[ "airElemental", "stormElemental" ],
 		[ "waterElemental" ]
 	],
+	
+	/// If set to true, this dwelling will not be selected as a replacement for random dwelling on map
+	/// Such dwellings have no restrictions on which tiles are visitable or blocked
+	/// For dwelling to be usable as a replacement, it must follow some additional restrictions (see below)
+	"bannedForRandomDwelling" : true,
 
 	/// List of guards for this dwelling. Can have two possible values:
 	/// Boolean true/false - If set to "true", guards will be generated using H3 formula:
@@ -20,3 +25,44 @@
 	]
 }
 ```
+
+## Replacement of random dwellings
+
+Existing maps may contain random dwellings that will be replaced with concrete dwellings on map loading.
+
+For dwelling to be a valid replacement for such random dwelling it must be:
+
+- block at most 2x2 tile square
+- one tile in bottom row must be visitable, and another - blocked
+
+Visible tiles (`V` in map object template mask) don't have any restrictions and can have any layout
+
+It is possible to make dwellings that don't fulfill this requirements, however such dwellings should only be used for custom maps or random maps. Mod that adds a new faction need to also provide a set of valid dwellings that can be used for replacement of random dwellings.
+
+Examples of valid dwellings:
+
+- minimal - bottom row contains one blocked and one visitable tile, second row fully passable
+
+  ```json
+  "mask":[
+      "AB"
+  ],
+  ```
+
+- maximal - bottom row contains one blocked and one visitable tile, both tiles on second row are blocked
+
+  ```json
+  "mask":[
+      "BB"
+      "BA"
+  ],
+  ```
+
+- extended visual - similar to maximal, but right-most column is fully passable. Note that blocked tiles still fit into 2x2 square
+
+  ```json
+  "mask":[
+      "BBV"
+      "BAV"
+  ],
+  ```