dapp-template fails to load in browser without MetaMask installed

Running the dapp-template with `npm run dev` and loading the local server in a browser that does not have MetaMask installed results in a blank black page and the following error in console:

```
Uncaught Error: Ethereum provider not found
at new MetamaskConnectClient (@gala-chain_connect.js?v=f678e57b:71205:17)
at setup (App.vue:37:24)
at callWithErrorHandling (vue.js?v=f678e57b:2308:19)
at setupStatefulComponent (vue.js?v=f678e57b:9985:25)
at setupComponent (vue.js?v=f678e57b:9946:36)
at mountComponent (vue.js?v=f678e57b:7301:7)
at processComponent (vue.js?v=f678e57b:7267:9)
at patch (vue.js?v=f678e57b:6782:11)
at render2 (vue.js?v=f678e57b:8064:7)
at mount (vue.js?v=f678e57b:6015:13)
```

Tested in Chromium on x86_64 Linux.

Suggest catching this error and displaying a call-to-action with link for the user to install MetaMask to use the application.