Change default text from Light to Regular (Source Sans Pro)

[DeniseColbert]

Please go ahead and make this change @arswright-alt-uk

@DeniseColbert Change is live for Review/QA at https://test2.freeukgenealogy.org.uk/ - a few notes:

Owing to issues with deprecated nodejs packages and a dependency issue ("grunt-sass@3.0.2 requires a peer of grunt@>=1 but none was installed." but npm show grunt version reports 1.0.4) this change was accomplished by linking the "Source Sans Pro (Light)" font files to "Source Sans Pro (Regular)" (ugly hack but I don't have a working SASS compiler and I had to install a deprecated version of nodejs just to get far enough along to encounter that bug).

The letter-spacing and font-size CSS properties have not changed, however, the Regular typeface will occupy more horizontal space (compare side-by-side with https://test3.freeukgenealogy.org.uk/ or the live site) which has an impact on how many elements appear - will leave it up to you whether you want to proceed with promoting this change.

[DeniseColbert]

To assess if we can implement without additional horizontal space.