Add Thunderbird start page
Merge pull request #252 from pascalchevrel/thunderbird_branch

Add Thunderbird start page
Add check for max length of strings, reduce classes size

**LangManager**
* Extract MAX_LENGTH from lang files
* Move ['python_vars'] to ['errors']['python'] to support more types of errors
* Add function countErrors
* Move functions for .po files into a new class
* Move error checks in separate functions (python, length)

**Utils**
* starsWith: accept array of strings as needle
* Use mb_strlen instead of strlen, add getLength

**GetTextManager**
* Functions to manage .po files originally in LangManager

**Views**
Expose number of errors in JSON, display errors in listsitesperlocale and errors view

Clean up phpDOC syntax in classes.