v2.0 Rewrite

[rhukster]

CHANGELOG

New

* Completely rewritten to be much more flexible
* New _class_ based problems architecture for unified problem definition and reporting
* New `onProblemsInitialized()` plugin event for 3rd party plugins to add their own problem checks
* New more intuitive theme based on Spectre.css to display problems
* Storage of problem state to allow for displaying in admin plugin
* Now with 3 states `critical`, `warning`, and `notice`.  Only critical will stop the site working.
* Added some new PHP module checks
* Added a new umask permission check