Let browsers open resources/elements in new windows/tabs.

Could take care of #9953
Removed hard coded "index.php" in manager assets
Removed hard coded "index.php" in relevant PHP files
Rebased
Removed hard coded "index.php" in manager assets

* origin/pr/11197:
  Rebased
  Removed hard coded "index.php" in relevant PHP files
  Removed hard coded "index.php" in manager assets
Let browsers open resources/elements in new windows/tabs.

* origin/pr/11320:
  Let browsers open resources/elements in new windows/tabs.
Make sure connector responses return application/json content type (unless not required)
Fix headers
Better check on ajax request than $_FILES
Make sure connector responses return application/json content type

* pr-11201:
  Better check on ajax request than $_FILES
  Fix headers
  Make sure connector responses return application/json content type (unless not required)
Updated changelog
Vertical "trees" PoC
Vertical "trees" PoC (tests with card layout)
Make use of card layouts for "entries" (added an xtype) for better performances
Just playing with styling
Just playing with styling (again) to make the nav looks more like the main menu
Enough styling!
Conditional entry
Yeah, styling again
And... again