- Change the default for the newWindow param from true to false, so
openPage() navigates in the same tab instead of opening a new one
- Accept a UUID string as the page argument in addition to a Page object,
avoiding the need to call penpot.getPage(uuid) first
- Add validation error when an invalid page argument is passed
Signed-off-by: Andrey Antukh <niwi@niwi.nz>