Add feature to add element in elements page of a project

Fixes project cloning

upgrade were not yet received. So we prepare for GPL by uniformizing
licence text keys to GPL-3+. Will move later to AGPL if all answers are
positive.

Conflicts:
	htdocs/projet/class/project.class.php

Conflicts:
	htdocs/projet/fiche.php

Fix: multicompany compatibility

Fix variable date property name, to be compliant with varaible naming
convention (create)
Add feature to shift task date when change project start date (option)
Add project start/end date on Project->Task View

Fix variable date property name, to be compliant with variable naming
convention (create)
Add feature to shift task date when change project start date (option)
Add project start/end date on Project->Task View