schemas FEATURE add schema getters from the context

Also check for the duplicities in the context when parsing a new schema.
diff --git a/tests/src/test_tree_schema_helpers.c b/tests/src/test_tree_schema_helpers.c
index 3dc7d7c..ac4e7bf 100644
--- a/tests/src/test_tree_schema_helpers.c
+++ b/tests/src/test_tree_schema_helpers.c
@@ -91,9 +91,9 @@
 
     /* revisions are stored in wrong order - the newest is the last */
     LY_ARRAY_NEW_RET(NULL, revs, rev,);
-    strcpy(rev->rev, "2018-01-01");
+    strcpy(rev->date, "2018-01-01");
     LY_ARRAY_NEW_RET(NULL, revs, rev,);
-    strcpy(rev->rev, "2018-12-31");
+    strcpy(rev->date, "2018-12-31");
 
     assert_int_equal(2, LY_ARRAY_SIZE(revs));
     assert_string_equal("2018-01-01", &revs[0]);