Merge pull request #70 from openalea/refactoring_vpltk

Refactoring vpltk

Do not forgt to take into account the different comments.
Change default drag and drop text for controls
Merge pull request #73 from gbaty/fix_control_drop_in_shell

Change default drag and drop text for controls
Add :checkbox: role to sphinx (Display a checkable checkbox, usefull for check lists)
Merge pull request #74 from gbaty/sphinx_role

Add :checkbox: role to sphinx
restore picklable curves remove by mistake
lpy model has a default input
fix error with name inside prepare_inputs
remove unused part in test