Test plugin functionality in 37 combinations of WP and PHP and fix found problems

* Test under WordPress from 3.2 to latest 4.0 and PHP from 5.2 to 5.5
* Fix plugin under non-latest WP versions
* Add test's buttons only in plugin's test editor, not in post's editor
* Use more styled headers at results page
* Use dashicons in admin only on WP that knows about it (>=3.8)
* Allow empty source in formula (with migration)
* Fix questions adding when scales, results and answers checked

Non-latest WP versions fixes (programmer's language):

* Avoid deprecated function in formula
* Add build status image into readme
* Remove another not-existing column from wp_posts under WP 3.6
* Check if we are at test screen for WP 3.2
* Move styles and scripts in editor and passer into head to fix under WP 3.2
* Fix test delete under WP 3.2 by clearing records cache
* Remove 3rd unused param from save_post subscription
* Avoid WP_Post in Test Editor
* Avoid direct usage of WP_Post class
* Avoid direct usage of WP_Screen class
* Fix minor notice under old WP version
* Add type=text to all inputs to fix ugly inputs under old WPs

git-svn-id: https://plugins.svn.wordpress.org/wp-testing/trunk@1020440 b8457f37-d9ea-0310-8a92-e5e31aec5664