Override sphinxdoc.css to put sidebar on the left

[sbesson]

Following @pwalczysko suggestions, this PR modifies the generic sphinx_theme
to move the sidebar on the left-side of the window.

[hflynn]

Handily, this will cover the BF docs too, won't it? Looks good on omero5-staging 👍

[sbesson]

Yes any built Sphinx documentation using this theme (i.e. all our deployed HTML documentation) should be modified by this).

[hflynn]

Checked on all the staging pages and looks good to me. Happy to merge once @pwalczysko confirms he's happy too.

[pwalczysko]

Very happy with this. Ta

[manics]

On a narrower screen:

[hflynn]

Damn! I'd noticed there wasn't a line dividing the content any more but not that it had consequences for narrower screens. I'll leave @sbesson to play with the settings in a new PR next week. Unless you want to try @manics ?

[hflynn]

Actually, I think this may be an issue with the breadcrumbs at the top - the sidebar is being offset rather than being underneath the additional sub-section. We may need to turn them off unless there is a way to make only show 2 levels of hierarchy.

[sbesson]

I can reproduce the issue indeed but I am having trouble identifying and fixing what is wrong. At this point, I would rather defer to someone with a deeper knowledge of CSS than myself to try and fix this.