Remove all vertical padding on the top and bottom of filters

Going to add this to contained elements instead so elements stack inside grey boxes sensibly
Put vertical whitespace onto form elements
Remove one level of indentation

I'm trying to restructure the css a bit to make it easier to add new input types to it when required. This commit de-nests some of the SCSS to make it easier to read.
Take .filter, .radio-filter, .checkbox-filter and .text-filter out of .filter-form scoping.
Change comment to make it more understandable
remove superfluous 'px' from '0px'
fix indentation
Move some input styles out of desktop only