Introduce the landing screen for kwallet

[rmallols]

As part of our very first task, we want to be able to define a basic layout, based on two columns:

• left: To create new wallet
• Right: To login to existing wallet.

Don't worry about adding images / buttons yet. Just build a screen with two sides, and some text on each.

BONUS: Try to centre the text (both horizontal and vertically speaking).

[rmallols]

Technical guidance:

Try to master as much as possible the flex-box technology, as it will be very important towards building complex UIs in the future. https://css-tricks.com/snippets/css/a-guide-to-flexbox/