[QuickSignPDF] Allow saving signatures locally to user machine and load them afterwards

[mkhatib]

The UX of this could vary but the simplest way right now is to:

• Let the user draw on PDF like usual
• Let them select the elements of a signature (all the lines)
• Click a button to save selected elements as a reusable element
• Convert the selected objects to JSON and store them in localStorage
• On loading the page load whatever in localStorage and put it in a dropdown kind of component
• When selected we load the JSON into the current page