New Tasks

This PR adds some custom Phing tasks, as follows:

* `phingy:assets:wordpress:addsalt`
* `phingy:assets:sass:update`
* `phingy:assets:sass:watch`
* `phingy:assets:browserify`
* `phingy:assets:watchify`
* `phingy:assets:uglifyjs`

The base namespace has also been switched to `Tev`, and the code now uses PSR-4 autoloading.