[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
Give the focus to the editor when the window is active
Enable french translation
Remove debug data
Fix responsive paper view

Display and hide correctly the left panel
Merge pull request #126 from tdurieux/fix_web_client

Fix and improve the web client
Bump dependency versions

Both tiscaf and diffson have been released, the SNAPSHOT versions are no
longer available.
Migrate common component to spray

This is the first big step of migration to spray server. The common
bundle entirely relies on spray and not on tiscaf anymore.
The class hierarchy was pretty much simplified for the Rest API, there
is no split between synchronous/asynchronous or
standard/authenticated/role HLet.

The interface to CouchDB was also cleaned up and is available to any
person extending the Rest API.
Migrate core module to spray
More work for the core component
Migrate compiler module to spray
Migrate the synchronization module to spray
Migrate web client to spray
Improve spray handling