TMDM-6803: "Staging Area : Progress and Stats do not reflect Match&Merge phase"

Switch to an 'infinite' progress bar that runs until validation completes.
Fixes minor UI glitches (cancel button not in the middle).
Improves automatic autorefresh=false on close tab (hooks to the JS event on tab close).
Fix cancel wrong behavior due to missing callback for REST client.
(https://jira.talendforge.org/browse/TMDM-6803)
TMDM-6803: "Staging Area : Progress and Stats do not reflect Match&Merge phase"

Refactors concept list to:
* leverage Metadata API
* actually take into account language.
(https://jira.talendforge.org/browse/TMDM-6803)