[scheduler] Allow to mark some events as resizable but not all

[flaviendelangle]

In this PR:

• Add a resizable?: boolean | 'start' | 'end' property to the CalendarEvent property
• In all the views with resizing, make sure the Event resizing is enabled when needed (the resizable property should take precedence over the top level prop)
• If resizable equal start or end then only the right side should be resizable.