New placeholder and changes to 2 existent placeholders!

[BlitzOffline]

I've added the following placeholder:

- %world_total_chunks_<world>%       # Gets the loaded chunks count in a world

I've also made some changes to existent placeholders to better align them with the Server placeholders:

- %world_entities_<world>%           -->  %world_total_entities_<world>%
- %world_entities_living_<world>%    -->  %world_total_living_entities_<world>%

Also, the values of total placeholders (the 3 mentioned above), are now cached for 1 minute. This is also aligned with the Server expansion which does the same.