Remove sources folder - add a download mechanism

[lapineige]

Hosting the sources is not a good idea > much better to download them on install, and check the hash. (As advised by @genma : https://forum.yunohost.org/t/fr-en-shaarli-app-lets-remove-the-dust/2200/11)

The sources should not be included in the repo, but downloaded during the installation (as wallabag app does it)

• [x] Remove sources folder https://github.com/YunoHost-Apps/shaarli_ynh/commit/702cc31ed212fd4b97a6ade301492928808a3068
• [x] Add the download process
• [x] Implement checksum test

This can be enhanced #17

[lapineige]

Let's use 0.8 version. https://github.com/shaarli/Shaarli/releases/tag/v0.8.0 SHA256sum of the tar.gz file: 9c87ee28e2686bfd7e78197ed04d3cd99de850c504fb5675df486761a80b2510

[lapineige]

Done. I finally used version 0.8.3. Closing.