Somewhat major improvements

I noticed that when an upgrade research (eg. Battleship lv.1 - lv.2) is completed, units of that type (eg. Battleship lv.1) are automatically upgraded to the next level.

In real life, that does not happen, older units are either upgraded at a modification center, or scraped for resources.

So I suggest these improvements:

1. Stop automatically upgrading

2. Add the option to upgrade units, which would take less time and resources, but can only be upgraded once

3. Add the option to scrap units, which take half the time to do so as building a new one, and give 70-90% of resources back

4. Add Scrapyards that need to be built on a province to scrap something on that province, they would need to be built with shipyards to scrap ships, infrastructure to scrap armor, etc.* **

5. Add Modification Centers that need to be built on a province to upgrade something on that province, they would need to be built with shipyards to upgrade ships, infrastructure to upgrade armor, etc.***

* Scrapyards would not need to be built with anything else for scrapping anything that only needs an Industrial Complex to be built

** Infantry and Militia could be retired without a Scrapyard

*** Infantry and Militia could be retrained (upgraded) at Barracks an unlimited amount of times, until they reach the last level of course