Automatically list of available courses on the home page

[szabgab]

Right now on the front page there is only one button to "Start Learning Spanish" which comes from apps/web/src/routes/index.svelte As we add more languages we should be able to list all the available languages without updating the source code for every language. We should be able to create the list of available languages from the content of the apps/web/src/courses/ directory.

This will be also useful for people who develop languages and have the languages on their computer, before they become pulic.

[kantord]

I would add some additional requirements:

• It should be possible to hide courses. Currently we have courses that are part of the build system but are not visibly linked. This is useful because this way people can share work-in-progress courses with other people without officially releasing them to the public
• It should probably be possible to sort the languages based on popularity. Right now we don't have analytics so this would be based on publicly available statistics about the language
• It should be possible to filter and group the courses based on source language

[szabgab]

I would probably go with two selectors or two filters. One for source and one for target language.