Rename "shadowLocale" to "shadowBaseLocale".

[Quehnie]

Q	A
Bug?	no
New Feature?	no
SuluArticleBundle Version	2.3.0
Sulu Version	2.3.0

Actual Behavior

There is a different variable naming for pages and articles with activated shadowLocale / shadowBaseLocale.

Expected Behavior

Use the same variable name (because canonical-tag is influenced by it)

Steps to Reproduce

Create a page and an article with Shadow-pages and check the shadowBaseLocale variable.

Possible Solutions

A quickfix is to default the variable like shadowBaseLocale|default(shadowLocale|default())