Rework model, of CheService and renamed it to ChePlugin. 
Replace features hosting to apache server to be able to host plugin files and avoiding having model files for Go lang.
Host YAMLs instead of JSONs. Downloads and parse ChePlugin YAMLs instead of JSONs from the marketplace.
Improve unit tests coverage. 
Add support of Che Server protocol and path, so it is possible to run Classic GWT IDE in Workspace Next now.
Signed-off-by: Oleksandr Garagatyi <ogaragat@redhat.com>