Shallow water tiles rework

[AVeryCoolSpider-PL]

Describe the content or mechanics you are proposing.

I want the shallow water tiles to work like ores, that is to cover the floor it is placed on and not have either sand or dark sand below, excluding some floor tiles, like snow or ice.

Describe how you think this content will improve the game. If you're proposing new content, mention how it may add more gameplay options or how it will fill a new niche.

This will add much more variety to rivers and smaller lakes; however many maps in the campaign would require rework if this gets implemented, not to mention numbered sectors.

Before making this issue, check the boxes below to confirm that you have acknowledged them.

• I have checked the Trello to make sure my suggestion isn't planned or implemented in a development version.
• I am familiar with all the content already in the game or have glanced at the wiki to make sure my suggestion doesn't exist in the game yet.
• I have read README.md to make sure my idea is not listed under the "A few things you shouldn't suggest" category.