Add default! to all settings variables

[meowsus]

Since the load order in app.scss is:

@import "scss/helper/flexiblegs-settings";
@import "bower_components/flexiblegs-scss/flexiblegs-scss";
@import "scss/helper/flexiblegs-scss-plus";

Wouldn't it be more useful to define all variables in flexiblegs-settings.scss as default! so that the host application could remove/modify these settings?

A few use cases would be:

• I want to change the default breakpoint names / values
• I want to change the row/column numbering
• I need to support IE8, so I want to drop the flexbox prop

Just to name a few.