Several improvements and refactoring

* Add total size of backups on the settings modal Fixes issue #255 
* Fixed a bug in one of the colorbox display functions that was causing the error messages to not be displayed
* Fix incorrect translation file names
* Add a constant for PHP version and use that in the version chek
* Fix a typo in a user message

* Major changes to the schedules code - prefixed our custom intervals with hmbkp_, which required a search and replace throught the plugin to rename all instances.
* Added a function to filter out our schedules from wp_get_schedules which is used when listing out the schedules on the admin side.

* Update Docblocks