Remove ember-component-css, drop Ember 2.18 support (#474)

* Remove ember-component-css from dependencies

`pod-styles` was breaking embroider, and pods are recommended against now anyway, especially with component colocation. With this in mind, I moved ember-component-css to devDeps, and moved the styles to the styles directory.

* Drop Ember 2.18 support

Author: RobbieTheWagner

.travis.yml

@@ -52,8 +52,7 @@ jobs:
       script: yarn test:test-apps
 
     - stage: versioned tests
-      env: EMBER_TRY_SCENARIO=ember-lts-2.18
-    - env: EMBER_TRY_SCENARIO=ember-lts-3.4
+      env: EMBER_TRY_SCENARIO=ember-lts-3.4
     - env: EMBER_TRY_SCENARIO=ember-lts-3.8
     - env: EMBER_TRY_SCENARIO=ember-lts-3.12
     - env: EMBER_TRY_SCENARIO=ember-lts-3.16

addon/styles/addon.scss

@@ -5,15 +5,21 @@ $site-container: 1400px;
 @tailwind components;
 @tailwind utilities;
 
-@import './components/docs-brand-colors';
-@import './components/docs-btn';
-@import './components/docs-container';
-@import './components/docs-md';
+@import './tailwind/components/docs-brand-colors';
+@import './tailwind/components/docs-btn';
+@import './tailwind/components/docs-container';
+@import './tailwind/components/docs-md';
 
 @import './utilities/masks';
 @import './utilities/nudge';
 
-@import 'pod-styles.scss';
+@import './components/docs-header-search-box';
+@import './components/docs-hero';
+@import './components/docs-keyboard-shortcuts';
+@import './components/docs-viewer-x-current-page-index';
+@import './components/docs-viewer-x-nav';
+@import './components/modal-dialog';
+
 @import 'syntax';
 
 // Figure out how to do this in tailwind