Various optimizations.

+ Make PT Sans as the default font.
+ Disable text-rendering: optimizeLegibility because of the double-bold bug on Firefox, iOS, etc. ( see http://wordius.com/tread-carefully-with-optimize-legibility/ )
+ Disable Tahoma font to make the website look more coherent.
Various improvements. Read details please.

+ Changed the base font of the whole website to PT Sans. More readable and clean. Also much more compatible with mobile devices.
+ A LOT of changes and enhancement for fonts, line heights and text reading in general.
+ Template adapted to fit the needs for the better font task.
+ Various optimizations for the SCSS files.
+ Cleanup for code that is not more needed after the changes mentioned before.