split base styles into _base, fonts into _fonts

Signed-off-by: Erica <e@energy7.com>
split app.scss and global.scss

Signed-off-by: Erica <e@energy7.com>
split out _mixins

Signed-off-by: Erica <e@energy7.com>
rename app.scss to theme.scss

Signed-off-by: Erica <e@energy7.com>
Move typography into base

Signed-off-by: Erica <e@energy7.com>