Issue1408 update readme

[lucasverleyen]

Fixes #1408

[lucasverleyen]

!! When #1452 is merged, I'll also add the logo to the readme.

[lucasverleyen]

The list of papers with applications of IDEAS becomes rather long, a bit too long to include in the README.
@annadellisola had the good suggestion of referring to the citations and/or metrics on the website of the paper: https://www.tandfonline.com/doi/citedby/10.1080/19401493.2018.1428361?scroll=top&needAccess=true. Consequently, we can remove the long list of applications and mention only the development papers.
@jelgerjansen what do you think?

[lucasverleyen]

I finished this issue. @jelgerjansen @annadellisola can you have a look? If you would like to see the online preview of the readme, you can check this link: https://github.com/lucasverleyen/IDEAS/tree/issue1408_updateReadme

As we agreed this morning, I removed the Applications of IDEAS section, because the list of papers is too long. Additionally, I think that adding a list of development papers does not bring added value. We'd better include those papers in the User's Guide and just write in the general readme that the models are documented properly. If you agree with this as well, I would add the papers in #1445.

2 notes:

1. This PR includes some paths that do not exist yet, but takes into account Update user's guide #1445. If more convenient, I can merge Update user's guide #1445 with this PR, so only one PR is left.
2. We need to update the version number and the part on the release history when we update to v4.0.0

[lucasverleyen]

I have merged this PR in #1445, such that #1445 and #1450 can be addressed together. Consequently, I'll close this PR.