Add lang + ref tags to frontmatter

Those are fields used by the language switcher to correlate pages across
different languages, even if they have different names/paths/titles.
They are generated with the prepare_for_translation.py script.

developer/code/code-signing.md

@@ -1,6 +1,8 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/code-signing/
+ref: 51
 title: Code Signing
 ---
 

developer/code/coding-style.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/coding-style/
 redirect_from:
@@ -6,6 +7,7 @@ redirect_from:
 - /doc/CodingStyle/
 - /wiki/CodingStyle/
 - /trac/wiki/CodingStyle/
+ref: 53
 title: Coding Style
 ---
 

developer/code/license.md

@@ -1,10 +1,12 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/license/
 redirect_from:
 - /en/doc/license/
 - /doc/QubesLicensing/
 - /wiki/QubesLicensing/
+ref: 52
 title: License
 ---
 

developer/code/source-code.md

@@ -1,10 +1,12 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/source-code/
 redirect_from:
 - /en/doc/source-code/
 - /doc/SourceCode/
 - /wiki/SourceCode/
+ref: 54
 title: Source Code
 ---