Upgrade php version

[malukenho]

Changes done here (Will need a major release):

• Upgrade php version to >=5.5
• Use psr-4 autoload schema
• Use of ::class
• Use Array short syntax

[mwillbanks]

@malukenho looks good - literally was something I was going to be attempting to get to for say the last 6+ months. I'll merge this in a bit later today; I would like to also get some of the other issues completed but since this would cause the largest breaks I think I'll merge this one first.

[mwillbanks]

I've merged this into the develop branch for now, we'll work through this a bit more until the remainder of the PR's are included and then we can look to release.