Fix build error and warnings

Author: jahn96

.eslintignore

@@ -2,4 +2,5 @@ node_modules
 dist
 coverage
 **/*.d.ts
-tests
+tests
+_temp_extension

.eslintrc.js

@@ -6,6 +6,19 @@ module.exports = {
     'plugin:prettier/recommended',
     'plugin:react/recommended'
   ],
+  settings: {
+    react: {
+      createClass: "createReactClass", // Regex for Component Factory to use,
+                                         // default to "createReactClass"
+      pragma: "React",  // Pragma to use, default to "React"
+      fragment: "Fragment",  // Fragment to use (may be a property of <pragma>), default to "Fragment"
+      version: "detect", // React version. "detect" automatically picks the version you have installed.
+                           // You can also use `16.0`, `16.3`, etc, if you want to override the detected value.
+                           // default to latest and warns if missing
+                           // It will default to "detect" in the future
+      flowVersion: "0.53" // Flow version
+    }
+  },
   parser: '@typescript-eslint/parser',
   parserOptions: {
     project: 'tsconfig.json',

src/CodeSnippetDisplay.tsx

@@ -462,7 +462,7 @@ export class CodeSnippetDisplay extends React.Component<
     target.addEventListener('mousemove', this.handleDragMove, true);
 
     // since a browser has its own drag'n'drop support for images and some other elements.
-    target.ondragstart = () => false;
+    target.ondragstart = (): boolean => false;
 
     event.preventDefault();
   }

src/FilterTools.tsx

@@ -41,15 +41,15 @@ export class FilterTools extends React.Component<
     this.filterSnippets = this.filterSnippets.bind(this);
   }
 
-  componentDidMount() {
+  componentDidMount(): void {
     this.setState({
       show: false,
       selectedTags: [],
       searchValue: ''
     });
   }
 
-  componentDidUpdate(prevProps: IFilterSnippetProps) {
+  componentDidUpdate(prevProps: IFilterSnippetProps): void {
     if (prevProps !== this.props) {
       this.setState(state => ({
         selectedTags: state.selectedTags