Separated the module "ext.uploadWizard.page"

* It allows depending on ext.uploadWizard without automatically calling createInterface and thus without immediately touching the DOM.
* In PronunciationRecording extension we can be dependent on the "ext.uploadWizard" module without calling the method "createInterface()".
* It allows easily passing in a different config to mw.UploadWizard.
* It will be helpful in the long run if and when some components of UploadWizard are merged into the core.
* Made some documentation improvements.

Bug: 49991
Change-Id: Id5c21e9aae93f642ad2114ffcfe195fe1c115aad