refactor(cc-dark-theme): organize styles in several files

Until now we had a single file for the dark theme styles with ~2500
lines, with several sections which were marked with CSS comments.

This CL separates this file into several ones to improve its
maintainability, using the folder structure suggested by
https://sass-guidelin.es/#architecture.

Fixed: twpowertools:21
Change-Id: I0c1741f58b470085c0a499b32aa64feb43d8ad31
diff --git a/src/ccDarkTheme/components/_action-bar.scss b/src/ccDarkTheme/components/_action-bar.scss
new file mode 100644
index 0000000..9bf28fa
--- /dev/null
+++ b/src/ccDarkTheme/components/_action-bar.scss
@@ -0,0 +1,15 @@
+.material-content .action-bar material-button,
+    ec-bulk-actions material-button,
+    ec-back-button material-button,
+    .sort-options material-button {
+  color: var(--TWPT-subtle-button-background)!important;
+}
+
+.material-content .action-bar .review-button.reviewing {
+  color: #1a73e8!important;
+  background: #dae7ff!important;
+}
+
+.material-content .action-bar material-button.starred {
+  color: var(--TWPT-starred)!important;
+}