Add react-i18next for multi-language support (#917)

This is a rough start on adding react-i18next. I'll be working on adding
more translatable strings and translations in the coming days. I'm going
to need to wrap class components in HOCs, so let me know if there's
something I should be fixing before doing that. I'm thinking now to keep
the exported class names exactly the same, and rename the existing
classes by prefixing an `I` (for internal). For example:

```
export default class AppToolbar ...
```

becomes

```
class IAppToolbar ...
const AppToolbar = withTranslation()(IAppToolbar);
export default AppToolbar;
```

I'll be able to contribute Japanese strings (I've talked to a couple
people on my team and they'll be happy to help as well), so that's the
language I decided to go with in this PR.

Closes #746

---------

Co-authored-by: Ko Nagase <nagase@georepublic.co.jp>
Co-authored-by: Harel M <harel.mazor@gmail.com>

src/components/_DeleteStopButton.tsx

@@ -2,21 +2,26 @@ import React from 'react'
 
 import InputButton from './InputButton'
 import {MdDelete} from 'react-icons/md'
+import { WithTranslation, withTranslation } from 'react-i18next';
 
 
-type DeleteStopButtonProps = {
+type DeleteStopButtonInternalProps = {
   onClick?(...args: unknown[]): unknown
-};
+} & WithTranslation;
 
 
-export default class DeleteStopButton extends React.Component<DeleteStopButtonProps> {
+class DeleteStopButtonInternal extends React.Component<DeleteStopButtonInternalProps> {
   render() {
+    const t = this.props.t;
     return <InputButton
       className="maputnik-delete-stop"
       onClick={this.props.onClick}
-      title={"Remove zoom level from stop"}
+      title={t("Remove zoom level from stop")}
     >
       <MdDelete />
     </InputButton>
   }
 }
+
+const DeleteStopButton = withTranslation()(DeleteStopButtonInternal);
+export default DeleteStopButton;