Add 'Import from' action on doctype layout definition

Today, a user as to redo all layouts for a document type even when they are very similar.
A quick way to import from a already created layout would improve layout creation and even updating (when a user update one layout and wants to propagate it to other layouts)

UX

• Button "import from", on layout right panel, on bottom
• On click/tap, open popup with list of doctype layouts that can be imported (in future, import from JSF layouts will also be present, not on scope for the ticket)

Import action

• User picks the intended layout
• Element is clone with targeting layout name