Prefix partial LESS source files with underscore

Closes #4907

_config.yml

@@ -11,7 +11,7 @@ pygments:         true
 permalink:        pretty
 
 # ensures SCSS files are compiled
-include:          [_*.scss]
+include:          [_*.scss, _*.less]
 
 # used in building icon pages
 icon_meta:        src/icons.yml

less/extras.less

@@ -1,2 +0,0 @@
-// Extras
-// --------------------------

less/font-awesome.less

@@ -3,15 +3,15 @@
  *  License - http://fontawesome.io/license (Font: SIL OFL 1.1, CSS: MIT License)
  */
 
-@import "variables.less";
-@import "mixins.less";
-@import "path.less";
-@import "core.less";
-@import "larger.less";
-@import "fixed-width.less";
-@import "list.less";
-@import "bordered-pulled.less";
-@import "spinning.less";
-@import "rotated-flipped.less";
-@import "stacked.less";
-@import "icons.less";
+@import "_variables.less";
+@import "_mixins.less";
+@import "_path.less";
+@import "_core.less";
+@import "_larger.less";
+@import "_fixed-width.less";
+@import "_list.less";
+@import "_bordered-pulled.less";
+@import "_spinning.less";
+@import "_rotated-flipped.less";
+@import "_stacked.less";
+@import "_icons.less";

src/assets/font-awesome/less/font-awesome.less

@@ -2,15 +2,15 @@
 ---
 {% include code/license.css %}
 
-@import "variables.less";
-@import "mixins.less";
-@import "path.less";
-@import "core.less";
-@import "larger.less";
-@import "fixed-width.less";
-@import "list.less";
-@import "bordered-pulled.less";
-@import "spinning.less";
-@import "rotated-flipped.less";
-@import "stacked.less";
-@import "icons.less";
+@import "_variables.less";
+@import "_mixins.less";
+@import "_path.less";
+@import "_core.less";
+@import "_larger.less";
+@import "_fixed-width.less";
+@import "_list.less";
+@import "_bordered-pulled.less";
+@import "_spinning.less";
+@import "_rotated-flipped.less";
+@import "_stacked.less";
+@import "_icons.less";