[fix #124] Make default API prefix relative

When using \BlueLaTeX from behind a proxy, if the API prefix is
absolute, then it might lead to some problems because the client send
the request to `/api`.
This is a problem iF \BlueLaTeX is not accessed at the root before
the proxy rewrites the URL.
Merge branch 'satabin-fix/wrong-default-api-path'
Fix file change

The content of the page is not anymore deleted when the user change the
file.
Change default settings of Ace Editor

Change the tab size
Remove key binding of snippet
Improve tooltips translation