Refactor: reduce usage of absolute paths on website

[dellagustin]

This issue is a follow up of #100 ,

See the following comments:

• https://github.com/InnerSourceCommons/innersourcecommons.org/issues/100#issuecomment-590076797
• https://github.com/InnerSourceCommons/innersourcecommons.org/issues/100#issuecomment-590089340
• https://github.com/InnerSourceCommons/innersourcecommons.org/issues/100#issuecomment-590091217

#100 will be fixed with #99, but it would be still good to revert the absolute paths to relative paths.

Issues

• [x] Assets from _head.html loading from absolute url - 925536f27bb6cacb5a87162267d09b57e926edca - #102
• [ ] Logo is loading from absolute url
• [ ] Navigation links are using absolute urls
• [ ] About this site section (footer?) is using absolute url
• [ ] Services section is using absolute url

[rrrutledge]

Thanks for opening this issue, @dellagustin