fortify condition on app:projectDirectory handler
handle an initial capture mode without actions

In this capture mode, we take screenshots using the dedicated
key 'F7', we create necessary files and modules except for
mouse actions, that we will introduce later.
Add utility functions for handling paths
better handling background model default values
save mouse position when taking a new screenshot
stop the capture mode with escape key
Add the possibility to remove the selected screen

There is some limitation with this initial delete mode :
- it is used only in capture mode.
This will be enhanced in an upcoming patch
- it doesn't remove the file from the hard drive
the screen is moved to a ready-to-be-removed list.
The files relating to this list's screen should be removed when
we click on the save button.
Merge branch 'next' into next-capture-mode

Conflicts:
	dahu/core/app/scripts/dahuapp.js
	dahu/core/app/scripts/modules/utils/paths.js
Merge branch 'next' into next-capture-mode

Conflicts:
	dahu/core/app/scripts/dahuapp.js
migrate some functions to screencast controller
create non existing img dir when taking capture
correct two minor typo errors
Merge branch 'next-capture-mode' into next