ux(): fixed issue with cach buster for temlpates, and updated on hover style for sidemenu to look better

fix(forms): reverted back to old checkboxes as the new ones are broken and missing clear state, fixes #4096

Matt weekend ui

ux(): added lines backgrounds, did not add them to the page background, could not make them look good / fit in without being distracting

ux(): tweaks and polish, and also simpifying width classes, gf-size-xxx and gf-size-max-xx are now width-(1-30), and max-width-(1-30)

created secondary button style, added a couple of variables, played with the plugins page to get the underline in place. Worth a look, but check that I was building everything properly :)