Generic schema for CMS Management: manage sites, not CMSs

[MacJoom]

As of now the schema is taken from the CMS Name in the CMS Management. This fails if you change the CMS Name to something like Joomla1 and Joomla2 because you want to migrate from 2 Joomla-Sites. Present there are 2 schemal files: joomla-ccm.json and wordpress-ccm.json. The CMS Management entry needs a field for the CMS Type, at present 'Joomla' and 'Wordpress'. Better a dynamic solution that offers the schemas present int src/schema folder.
For testing purposes you can copy the .json to your CMS Name, e.g. joomla1-ccm.json

[HermanPeeren]

Instead of CMSs we need a list of sites.

Each site:

• Is built upon a specific CMS (dropdown select from the CMSs that are defined - now: Joomla and WordPress).
• Has a name.
• Has a URL.
• Has credentials (of the web services API).

The migration is from a site to a site. Then you can also migrate from a Joomla site to a Joomla site.