juggler: depends_on algorithms (#607)

### Briefly, what does this PR introduce?
As of juggler-9.1, juggler depends on algorithms as an external package,
however that doesn't work with the algorithms CMake targets as defined,
and it must use the vendored version.

As of juggler-14, juggler *requires* an external algorithms install.

packages/juggler/package.py

@@ -175,6 +175,9 @@ class Juggler(CMakePackage):
 
     depends_on("cppgsl")
 
+    # FIXME change to @14: when released
+    depends_on("algorithms", when="@13:")
+
     depends_on("k4fwcore", when="@13:")
     depends_on("k4actstracking", when="@13:")