Renders mode changed and renamed file merge request diff
viewers on the frontend.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/52607

This caused many pain points when working with it.
Part of the data was camel cased the other snake case.
Other parts where snake case & then getting converted in components,
this conversion has the potential for leaking memory.

This changes that & makes it consistent with what it returned from the
API, snake case.

This fixes files that are collapsed by default not expanding
when the expand all button is clicked.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53866

Pre-request to https://gitlab.com/gitlab-org/gitlab-ce/issues/48956

This file tree displays all the diff files in a tree like format
Each file is taken and converted into a tree with folders
Each folder can be toggled open & closed
Clicking a file will scroll to the diff file & highlight with a glow affect

Searching the tree list will search only files & return a list of the
files without any folders

Each file row contains an icon to show changed, new file or deleted
Each row will also contain the added & removed lines count

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14249

Detailed: Because of rewire we need to export a default empty object in our actions to prevent it to export the wrong default in karma. Vuex getters are global, and because the Vuex store uses several non namespaced moduled, there was already a getter named default, due to the same empty export.
In order to solve it I chose to namespace the module. Could also be fixed by importing the getters explicitly instead of all of them.