Implement creating a new XPage in the CM

Based on the the Create content functionality
A new XPage can be created using the '+ Add' button for adding new xPages, landing pages (old style / classic pages) and components (far right on the CM top bar). Adding a component in this way should open the left-side panel on the components tab.

See attached images (0510 through to 0560) and mockup starting from:
https://bloomreach.invisionapp.com/d/main?origin=v7#/console/19555213/409585311/preview?scrollOffset=0
or: https://bloomreach.invisionapp.com/share/N4WCV1BEUXC#/409585311_0500_Add_XPage