introduce a utility function in path :

getDahuFileFromDirectory : Get the name of the presentation file to
create when we create a new project, it is calculated from the name of the Directory.
introduce a Directory chooser window in the kernel
add the new project button in the menu
Handle the creation of a new project
Fortify conditions on screen view :

This is important for when we want to create a new project
with no screens on screencastn or when we initialize the workspace with
no screen.
Merge branch 'next' into next-new-project

Conflicts:
	dahu/core/app/scripts/dahuapp.js
	dahu/editor/src/main/java/io/dahuapp/editor/DahuApp.java
migrate utility functions to screencast controller

the function moved here is getDahuFileFromDirectory, used
to get the name of the presentation to create relating to
the given directory
factorize layout creation code

this code is used when we open an existing project
or when we create a new empty one.
Merge branch 'next-new-project' into next