Add tags, improve formulas editor and docs

* Prefix screenhots by zeros
* Remove session stuff to avoid openbasedir bug
* Update compatible up to WP 4.0
* Swap formulas and results columns in editor
* Add tags to test

git-svn-id: https://plugins.svn.wordpress.org/wp-testing/trunk@1029042 b8457f37-d9ea-0310-8a92-e5e31aec5664