Increase size of TUOS logo

[tdjames1]

The TUOS brand identity approved logo is currently displayed with a width of 250px. I'd suggest that this is too small because, at this size:

1. UoS shield motif is blurred
2. "Research Software Engineering" text is very small
3. UoS logo text is far smaller than heading text size (see also Heading text sizing #558)

I'd suggest increasing the width of the image to 281px, which is the width of the logo image used here: https://player.sheffield.ac.uk/, in addition to reducing the heading font size as suggested in #558.