(OUI Docs) Header Documentation

[KrooshalUX]

• [x] Remove references to Kibana Spaces
• [x] Remove references to Timelion App
• [x] Remove references to Graph App
• [x] Remove references to Machine Learning App
• [x] Change username from John Username to A. User for inclusivity
• [x] Replace logoElastic with logoOUI
• [ ] Replace links to Elastic blog

[KrooshalUX]

I have an open PR for this but not sure how to move this forward as I am blocked on making further commits @BSFishy

[KrooshalUX]

Blocked pending help with stalled PR