SASS Expansion, M&H Page Template

- template for mission & history page
- template css classes for:
  - left box, right box
  - blue / green background
  - page / post titles
- added box-sizing: border-box to all (*) tags
- expansion of the transition mixin (added variable for transition
property. / updated all classes using mixin)
- fix for the email signup box (not aligning properly)