XWIKI-12787: Keep new lines when PUT/POST text/plain

* Use IOUtils.toString() to convert from InputStream to String
* Add the possibility to have multi-lines plain text for adding multiple tags

XWIKI-12783: Add hidden property for pages in REST API

* return 'hidden' property when GET a page
* set 'hidden' property when PUT a page in 'application/xml'
* set 'hidden' property when PUT a page in 'application/x-www-form-urlencoded'

- Deprecated the translations for the type property

- Removed the property from the class, updated the sheet and template
- Added a migrator to delete existing properties in objects and migrating the old values to the new "terminal" property.

* Add missing @since

* Extend the page objects to be able to delete an application and its entries.

* add test

* Bulletproof the AWM wizard
* Extend ApplicationCreatePage page object to be able to create a page in a nested space
* Extend ApplicationsLiveTableElement to be able to check if an application created in a nested space is listed
* Bulletproof the #livetable Velocity macro by properly escaping the live table id depending on the context (HTML, JavaScript)
* Fix Prototype.js to be able to call $(id) with an id that contains backslash

* Fix tests.

* Fix tests.

* Add page object to access the children viewer (needed by AWM tests in enterprise)