Warn and prevent users from building a page that's beyond the size limit

In Skuid on Salesforce (SFX), it's possible to build and save a page that's larger than the character limit.

• Skuid's page composer should visually show a user how large the page is (its XML length) in comparison to how close they are to the limit.

• If the page's XML length is nearing the limit, the page composer should guide users towards the best practice of splitting new functionality into a separate page (leveraging page-include components).

• The page composer should disable the page composer's save button if the user's unsaved changes might generate XML that's too big to be saved correctly.

• The save process should validate the XML that's being saved before any data changes are made.