Reduce base font sizes across app by 1px

Looking at other websites that use system fonts, the default seems to be `14px`. We currently use `15px` which feels a little too big at the moment (in my opinion). This is just an idea so feel free to close it @awhildy 😄    
Before:   
![Screen_Shot_2016-12-02_at_1.46.25_PM](/uploads/4e287d3e66b1fe1dbac9999978594546/Screen_Shot_2016-12-02_at_1.46.25_PM.png)
After:   
![Screen_Shot_2016-12-02_at_1.46.02_PM](/uploads/09aed0952c25df214e8e5fb1404d6f4f/Screen_Shot_2016-12-02_at_1.46.02_PM.png)

See merge request !7905