EZP-23147: As a developer, I want to be able to write plugins for views

JIRA: https://jira.ez.no/browse/EZP-23147 (More PR to come to completely implement the story)

# Description

This PR is a follow up of #98 / [EZP-23012](https://jira.ez.no/browse/EZP-23012) which allows the developer to write plugins for any views in the Platform UI Application provided this view extends the base `eZ.View`.

Unlike the plugins for a view service added in #98, a plugin for a view does not need to implement any *eZ* base class (*interface*) excepting, of course, what is described in [the YUI Plugin documentation](http://yuilibrary.com/yui/docs/plugin/#advanced).

To be really useful, we'll need to have a way to override/inject/modify the JS templates. This will be tackled in a next story.

Note: this patch relies on what is provided by #98 which is not merged yet, so the PR is done against the feature branch of #98.

# Tests

unit tests
What is the reason you named a variable with the capital letter at the beginning?