Made Language.addFileExtension public, added a languageModified event, made DocumentManager update document's languages as necessary
Update the language name if the language changes
Forgot some places that should make the language as modified
Remove runs(...) in LanguageManager-test.js where it is unnecessary
Merge branch 'master' into dk/issue-2966

Conflicts:
	src/language/LanguageManager.js
Merge pull request #3051 from DennisKehrig/dk/issue-2966

Made Language.addFileExtension public