Use 404 status code for custom 404 page

Fixes #275 and #291.
Allow Cms Controller to set status code
Simplify logic, test + cert
Backend and frontend controllers now return a Response object and support setting the status code
Fix variable name in isset magic method
Merge pull request #321 from niclasleonbock/master

Fix variable name in isset magic method
Update DocBlock/function header for __set and __isset
Update CodeBase.php
Merge pull request #322 from niclasleonbock/master

Update DocBlock/function header for __set and __isset
Fixes #328 - Move Twig init to Controller constructor
Minify less files output if enabled
Merge pull request #332 from sl1nk3/develop

Minify less files output if enabled
Widgets no longer need to pass their config via options:
Update CHANGELOG.md