Split base styles into base.css

That way we can load this css in other projects to bring the basic stuff
such as normalize, navbar, notifications, custom scrollbars, and so on.

src/styles/main.sass

@@ -12,15 +12,12 @@
 @import _error
 @import _stats
 @import _search
-@import _base
-@import _notifications
 
 /* services, about, etc */
 @import _pages
 
 
 @import plugins/_jstree
-@import plugins/js_perfectscrollbar
 @import plugins/_js_select2
 
 /* CSS for pillar-font comes from fontello.com using static/assets/font/config.json */