Standardize all SCSS files to SASS format (less constraints).

Identified files:

./src/sass/_legacy/_phylo.scss
./src/sass/_legacy/_annotation.scss
./src/sass/fork-awesome.scss
./src/sass/modules/_layout.scss
./src/sass/modules/_form.scss
./src/sass/modules/_tree.scss
./src/sass/modules/_annotation.scss
./src/sass/components/_loading_spinner.scss
./src/sass/components/_grouped.scss
./src/sass/vendors/_include-media.scss
./src/sass/abstract/_members.scss
./src/sass/abstract/_variables.scss
./src/sass/base/_layout.scss
./src/sass/base/_reset.scss
./src/sass/base/_general.scss
./src/sass/base/_form.scss
./src/sass/base/_utilities.scss
./src/sass/base/_bootstrap.scss
./src/sass/base/_typography.scss
./src/sass/base/_animations.scss
./src/sass/base/_nav.scss
./src/sass/base/_placeholder.scss
./src/sass/themes/_abstract.scss
./src/sass/themes/monotony.scss
./src/sass/themes/greyson.scss
./src/sass/themes/herbie.scss
./src/sass/themes/_base.scss
./src/sass/themes/default.scss
./src/sass/themes/darkster.scss