XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Create modules xwiki-platform-wiki, xwiki-platform-wiki-api & xwiki-platform-wiki-default
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Move XWikiServerClassDocumentInitializer from oldcore to wiki-default
* Create xwiki-script
* First version of the API and of the implementation.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Create xwiki-platform-wiki-template modules.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Write xwiki-platform-wiki-template-api module.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Write xwiki-platform-wiki-template-default module.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Write xwiki-platform-wiki-template-script module.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Rename WikiDescriptor to Wiki.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Redo a clean API.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Implement the clean API.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Remove WikiAlias class. Make Wiki class more simple.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Create WikiPropertiesGroup.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Rename Wiki to WikiDescriptor.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Add the hidden field.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Rename WikiManager#getById() to WikiManager#get()
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Rename WikiDescriptor#get() to WikiDescriptor#getPropertiesGroup()
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Add WikiManager#getMainWikiDescriptor()
* Create WikiDescriptorBuilder
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Implementing tests...
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Implementing tests...
* Rename WikiPropertiesGroup to WikiPropertyGroup (thx to Eddy!)