Adding fig caption styling, correcting members overview semantics

Signed-off-by: Peter Hartree <web@peterhartree.co.uk>
Mobile navigation: more vertical space, larger font size

Signed-off-by: Peter Hartree <web@peterhartree.co.uk>
Mobile: add margin to .item component

Signed-off-by: Peter Hartree <web@peterhartree.co.uk>
Update OpenGraph logo

Signed-off-by: Peter Hartree <web@peterhartree.co.uk>
Changing navigation breakpoint

Signed-off-by: Peter Hartree <web@peterhartree.co.uk>
Add og:image tag to blog articles

Signed-off-by: Peter Hartree <web@peterhartree.co.uk>