update v17.5

"Discord Suggestions" is a short serie that will feature random prompts from
the #suggestions channel on our Discord Server.

The aim of this serie is to chop down the long suggestion list, without
having to wait a specific theme. 

Each batch will last 5-10 updates and is planned on a bi-monthly basis (~)

-
Since one of the requests was to add more terrain variation, I took the opportunity to redraw some of them, since I think they were a weakness of the whole asset

- Added a new grass + dirt tileset (2 colors)
- Added a new grass + water tileset 
- Updated the themes and single files with the new stuff

See you and happy game-making! :)