Converts some em length declares to px

In the process of converting length declares.
Converts some more em lengths to px
Converts rest of lengths to px
Converts some missed em declares to px
Adds more spacing for Frontpage preface links
Cloning a commit from master

546d15b2a98280e96540ad86199c2b3ebf95b174
Replaces em in twocol panel layout scss
Replaces colour variable declarations

Sass globbing can't read _colors.scss so replaces the variable usages
with raw hex.
Modifies line height year

Reduces the line height of the year title in the timeline, in narrow
layout by 10px.
Compiles production CSS
Revert "Adds margin for mobile layout to all regions"

This reverts commit 546d15b2a98280e96540ad86199c2b3ebf95b174.