[Frontend] Markup and CSS related to indicators; hover styles

open #442
https://github.jpl.nasa.gov/MissionControl/vista/issues/293

s-btn hover styling cleaned up;
Spacing, styles, etc. for indicators refined;
Constants, colors added to, cleaned up and normalized;
Animation code in _effects refactored;

platform/commonUI/general/res/sass/controls/_buttons.scss

@@ -66,7 +66,7 @@ $pad: $interiorMargin * $baseRatio;
 
     &:not(.major) {
         // bg, bgHov, fg, ic
-        @include btnSubtle($colorBtnBg, $colorKey, $colorBtnFg, $colorBtnIcon);
+        @include btnSubtle($colorBtnBg, $colorBtnBgHov, $colorBtnFg, $colorBtnIcon);
     }
     &.pause-play {
 
@@ -91,7 +91,7 @@ $pad: $interiorMargin * $baseRatio;
         &.paused {
             @include btnSubtle($colorPausedBg, pushBack($colorPausedBg, 10%), $colorPausedFg, $colorPausedFg);
             .icon {
-                @include pulse(1000ms);
+                @include pulse($dur: 1000ms);
                 :before {
                     content: "\0000EF";
                 }
@@ -269,14 +269,16 @@ $pad: $interiorMargin * $baseRatio;
     }
 
     .first {
-        .s-btn {
+        .s-btn,
+        &.s-btn {
             @include border-left-radius($controlCr);
             margin-left: 0;
         }
     }
 
     .last {
-        .s-btn {
+        .s-btn,
+        &.s-btn {
             @include border-right-radius($controlCr);
         }
     }