replace various SASS button.color-* extending by button-color-basic mixin

sass/base/_utils.sass

@@ -43,22 +43,25 @@
 			color: #666
 			+box-shadow(1px 1px 0 rgba(#444, .3))
 
+@mixin button-color-basic($type: 1)
+	$color: $main-color-color
+	$hover-border-color-darken-amount: 22%
+	@if $type == 2
+		$color: #64676C
+		$hover-border-color-darken-amount: 15%
+	background: $color
+	border-color: darken($color, 5%)
+	color: white
+	font-weight: 500
+	&:hover
+		border-color: darken($color, $hover-border-color-darken-amount)
+
 button, a.button
 	@include button-basic
 	&.color-1
-		background: $main-color-color
-		border-color: darken($main-color-color, 5%)
-		color: white
-		font-weight: 500
-		&:hover
-			border-color: darken($main-color-color, 22%)
+		@include button-color-basic
 	&.color-2
-		background: #64676C
-		border-color: darken(#64676C, 5%)
-		color: white
-		font-weight: 500
-		&:hover
-			border-color: darken(#64676C, 15%)
+		@include button-color-basic(2)
 	&.small
 		padding:  .5rem
 		font-weight: 700

sass/layout/_groupchat.sass

@@ -143,4 +143,4 @@
 		float: none
 		display: inline-block
 		padding: 7px
-		@extend .color-1
+		@include button-color-basic

sass/layout/_modal.sass

@@ -145,7 +145,7 @@ $header-modal-height : $menu-height
 			right: 2px
 			top: $header-modal-height +2
 			z-index: 2000
-			@extend .color-1
+			@include button-color-basic
 
 
 	&.new-users-modal

sass/layout/_profile.sass

@@ -109,9 +109,9 @@ $modal-postboard-post-height: 100%
 
 
 .follow
-	@extend .color-1
+	@include button-color-basic
 .unfollow
-	@extend .color-2
+	@include button-color-basic(2)
 
 
 .known-followers

sass/pages/_profile.sass

@@ -59,9 +59,9 @@
 		&.last-child
 			margin-right: 0
 		&.submit-changes
-			@extend button.color-1
+			@include button-color-basic
 		&.toggle-priv-key
-			@extend button.color-2
+			@include button-color-basic(2)
 	.secret-key-container
 		text-align: left !important
 		font-size: 1rem!important