Settings

> ### Dependencies:
>
> - [ ] front-end: input field, button (#8)
>
> - [ ] back-end: Endpoint to save settings (spec: #7, impl: #)

This issues consists of two steps

1. Add a link to the main navigation (settings, a cog icon or something similar) to the settings page

1. settings page

I believe the first part is self-explanatory, the settings page will be the place where the user can configure the application. Firstly, this means a way to add root directories in which the back-end searches for video files and a list of file extensions that should be included.


There are multiple ways to implement this page. It could be a separate html page, but keep in mind that duplicates the navigation. It could also be implemented as popover, either over the entire page or just as big as the content requires it to be. Just implement it the way you think is best, but always keep mobile support in mind.