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/dialogs/_keyboard-shortcuts.scss b/src/ccDarkTheme/components/dialogs/_keyboard-shortcuts.scss
new file mode 100644
index 0000000..047118b
--- /dev/null
+++ b/src/ccDarkTheme/components/dialogs/_keyboard-shortcuts.scss
@@ -0,0 +1,20 @@
+material-dialog .main.with-scroll-strokes table th {
+  color: var(--TWPT-primary-text)!important;
+}
+
+material-dialog .main.with-scroll-strokes table td {
+  color: var(--TWPT-primary-text-alt)!important;
+}
+
+material-dialog .main.with-scroll-strokes table tr,
+    material-dialog .main.with-scroll-strokes .shortcut {
+  border-color: var(--TWPT-card-border)!important;
+}
+
+material-dialog .main.with-scroll-strokes.bottom-scroll-stroke {
+  border-bottom-color: var(--TWPT-card-border)!important;
+}
+
+material-dialog .main.with-scroll-strokes.top-scroll-stroke {
+  border-top-color: var(--TWPT-card-border)!important;
+}