Add splash screens for Android and iOS

[rafmjr]

Added support for splash screens on mobile devices (Android and iOS). The standard manifest.json file was used to setup a basic screen displaying a white version of the logo on top of a green background, whereas the splash screen for iOS was a little more involved due to the lack fully support of PWA.

Prompting the user for installation should be supported by adding a Service Worker.

This should help to solve the issue [Add a splash screen #157](Add a splash screen )

[ubaldop]

hi @rafmjr, impressive, thank you for your contribution!
@mcicolella do you think shall be useful to introduce a Service Worker to make fd-vue-webapp fully PWA compliant?
I am not quite familiar about PWA proper setup.

@mcicolella are you able to test this PR on iOS?

[mcicolella]

@p3trur0 I don't have an iOS phone. Currently I'm testing mobile layout on Chrome with UA Spoofer.

[ubaldop]

@rafmjr would you like to help us in making this application a PWA? I am going to open an issue in minutes.
Moreover, are you familiar with any iOS simulator to test your Splash Screen addition?

[rafmjr]

@p3trur0 it would be my pleasure to help you with that issue. Now, regarding on how to test these splash screens in iOS, if you don't have an iPhone, you would need to install xcode and start a simulator from there.

[ubaldop]

@rafmjr glad to hear that! So, please, feel free to take #177.
Also, thank you for pointing out the xcode option for testing iOS splash screen.

So far I do not have a Macbook machine, however I merge this PR because personally it looks good to me.