Added a incubating project config option

This allows projects that are currently incubated to use oslosphinx

To use a project needs to set

'html_theme_options = {'incubating': True}'

in their sphinx conf.py

This is option reflected by changing the side bar to have a bar
at the top that shows 'Incubated Project'

Change-Id: Ib5a06ac1749fec475d326afe19f16fffb8c7d4a7