Broken backwards compatibility

[martinkrcho]

We have a bug in the extension core:
https://github.com/WPWhiteSecurity/wsal-extension-template/blob/master/core/class-extension-core.php#L57-L63

This prevents the most recent versions of extensions to load correctly if any of the older extensions is installed. We need to rename variable $core_settings to $extention_main_file_path.

While we're at it, please rename $extention_main_file_path to $extension_main_file_path both in constructor and the class property (notice 1 changed letter to fix spelling). Also $extention_plugin_name needs changing to $extension_plugin_name.

[sdobreff]

/cib

[create-issue-branch]

Branch issue-37-Broken_backwards_compatibility created!