Add xliff import for articles

[wachterjohannes]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Fixed tickets	none
Related issues/PRs	none
License	MIT

What's in this PR?

This PR add a command to import the articles from a xliff export.

Why?

It should be possible to import the file from a tool or a translation agency.

Example Usage

$ bin/adminconsole sulu:article:import export.xliff de --overrideSettings
Language Import
===============

Options
Locale: de
Format: 1.2.xliff
Override Setting: YES
---------------

Continue with this options? Be careful! (y/n) y
Continue!
 1/1 [============================] 100% 2 secs/2 secs 54.5 MiB

Import Result
===============
1 Documents imported.
0 Documents ignored.

To Do

• Add documentation page