WEB: Reorganization of the Ecosystem page
I changed the sections of the Ecosystem page, in a way that the pandas extensions are grouped together first, and the other sections emphasize how packages they are related to pandas. I merged two separate IO sections, and the IDEs with the development tools.

I added line breaks to very long lines, and improved a bit the styles.

Probably better to check the preview when ready, than the diff, as the diff will be long and difficult to follow as mostly every library is moved.

/preview Website preview of this PR available at: https://pandas.pydata.org/preview/pandas-dev/pandas/61657/community/ecosystem.html Thanks @datapythonista 