Webstorage plugin (localStorage was load as sessionStorage) (quasarframework#1326)

* Storing an empty string and getting it back produce a bad behavior.
There was a test for considering the value only if it contains at least 10 chars, but 9 is the correct number. As each key plus separator '"__q_strn|".length' contains 9 chars not 10. So getting a value from "__q_strn|" was returning "__q_strn|" instead of "".

* Should not it be validator instead of validation in QTree for tickStragegy props ?

* Webstorage plugin (localStorage was load as sessionStorage)

Author: erakis

src/plugins/web-storage.js

@@ -130,7 +130,7 @@ export const LocalStorage = {
     this.__installed = true
 
     if ($q.platform.has.webStorage) {
-      const storage = getStorage('session')
+      const storage = getStorage('local')
       $q.localStorage = storage
       extend(true, this, storage)
     }