configurable branding/white labelling

[andiempett]

The app should allow for simple, configurable changing of the colour schema and branding
currently its hard coded for JISC assets and wording.

examples
https://github.com/k-int/KBPlusG5/blob/main/kbplus/grails-app/views/layouts/base.gsp#L111
https://github.com/k-int/KBPlusG5/blob/main/kbplus/grails-app/assets/images/jisc-logo.png