For my new extension Copy2Clipboard i need 2 new hooks.

Changes proposed in this pull request:

• Add hook to add some navigation options: Now the developers of extensions have the chance to add additional navigation points. In my case, i add an COPY button.
• Add hook to add some jsonVars: In my case i need some translated texts in the javascript section. With this hook i can add this texts into the jsonVar script-tag and in my javascript code i can use this text with context.extensions.copy2clipboard.msg_good_more.

Pull request checklist:

• clear commit messages
• code manually tested
• unit tests written (optional if too hard)
• documentation updated - EN only!

Additional information can be found in the documentation.