Create json for experimental flags

In practice, this should help implement the flags without having to hardcode them

Author: JayPanoz

css/vars/experiments.json

@@ -0,0 +1,12 @@
+{
+  "experimentalHeaderFiltering": {
+    "description": "Attempts to filter out paragraphs that are implicitly headings or part of headers",
+    "scope": "RS",
+    "value": "readium-experimentalHeaderFiltering-on"
+  },
+  "experimentalZoom": {
+    "description": "Attemps to filter out elements that are sized using viewport units and should not be scaled directly e.g. tables, images, iframes, etc.",
+    "scope": "RS",
+    "value": "readium-experimentalZoom-on"
+  }
+}