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/_index.scss b/src/ccDarkTheme/components/_index.scss
new file mode 100644
index 0000000..6307f8f
--- /dev/null
+++ b/src/ccDarkTheme/components/_index.scss
@@ -0,0 +1,26 @@
+@forward 'drawer';
+@forward 'notifications';
+@forward 'tabs';
+@forward 'query-builder';
+@forward 'action-bar';
+@forward 'thread-list';
+@forward 'review-bar';
+@forward 'activity-panel';
+@forward 'thread-view';
+@forward 'stepper';
+@forward 'thread-composer';
+@forward 'profile-chart';
+@forward 'user-badge';
+@forward 'duplicate-thread';
+@forward 'buttons';
+@forward 'icon';
+@forward 'dialogs';
+@forward 'rich-text-editor';
+@forward 'thread-insert';
+@forward 'inputs';
+@forward 'menu';
+@forward 'popups';
+@forward 'canned-responses';
+@forward 'settings';
+@forward 'loading-spinner';
+@forward 'custom';