Move screenshots to Wiki

[doctorfree]

Note that you can decrease the size of this configuration by about 1/3 by moving the screenshots in ./screenshots/ to the Wiki or some other website. That's about 6.4MB users would not have to download. Maybe it's not important.

Right now there is no Wiki but that's easy to create in the repo settings. Then in the Ecovim README.md replace all the links to screenshots with the url to the Wiki. For example, replace:

![Dashboard](./.screenshots/6-alpha.png)

with

![Dashboard](https://raw.githubusercontent.com/wiki/ecosse3/nvim/.screenshots/6-alpha.png)

assuming you kept them in .screenshots in the wiki.

Please excuse this minor nit. I really like Ecovim.