[Editor] Add support for Character Sets

proto/src/main/proto/project.proto

@@ -9,6 +9,7 @@ message Project {
   repeated GameMapAsset maps = 3;
   repeated TileSetAsset tileSets = 4;
   repeated ImageAsset images = 5;
+  repeated CharacterSetAsset characterSets = 6;
 }
 
 message GameMapAsset {
@@ -29,4 +30,12 @@ message ImageAsset {
   required string uid = 1;
   required string source = 2;
   required string name = 3;
+}
+
+message CharacterSetAsset {
+  required string uid = 1;
+  required string source = 2;
+  required string name = 3;
+  required uint32 rows = 4;
+  required uint32 columns = 5;
 }