2706: *.storageManager.enabled;false => inactive

Controls the visibility of the "Options>Privacy & Security>Site Data" section.
I'd prefer to remove this completely because it only adds to the confusion about all the different storage types.
This is just an extension for localStorage (2705) with 3 methods: estimate(), persist() and persisted(). A site can ask for permission (?) to persist data which when granted basically just means that "Storage will not be cleared except by explicit user action" whereas otherwise when not persisted "Storage may be cleared by the UA under storage pressure." - I don't see a problem with that.
We'll keep 2706 inactive for now but might remove it in a future commit.

user.js

@@ -1449,8 +1449,8 @@ user_pref("network.cookie.thirdparty.sessionOnly", true);
  * [1] https://developer.mozilla.org/docs/Web/API/StorageManager
  * [2] https://developer.mozilla.org/docs/Web/API/Storage_API
  * [3] https://blog.mozilla.org/l10n/2017/03/07/firefox-l10n-report-aurora-54/ ***/
-user_pref("dom.storageManager.enabled", false); // (FF51+)
-user_pref("browser.storageManager.enabled", false); // (FF53+)
+   // user_pref("dom.storageManager.enabled", false); // (FF51+)
+   // user_pref("browser.storageManager.enabled", false); // (FF53+)
 /* 2707: clear localStorage and UUID when an extension is uninstalled
  * [NOTE] Both preferences must be the same
  * [1] https://developer.mozilla.org/Add-ons/WebExtensions/API/storage/local