More informative error message

If you have many models, it's useful to know which one is badly configured :)
Merge pull request #722 from loostro/master

More informative error message
Add basic Excel functionality
Added documentation and adjusted composer.json for the excel package
Fixing incorrect usage of the Doctrine ODM query builder
Fixing incorrect usage of the Doctrine ODM query object
Merge pull request #726 from robholmes/master

Fixing incorrect usage of the Doctrine ODM query builder
Updated some public to protected + fix missing space Japanse translation
Simplified the return statement
Merge pull request #725 from bobvandevijver/excel

Excel export of the list view
Fix 'es' translation
Merge pull request #728 from johnarevalo/patch-1

Fix 'es' translation
Removed unused code which generates PHP warnings
Merge pull request #740 from bobvandevijver/master

Removed unused code which generates PHP warnings
add preBindRequest($model) in indexAction of EditController and NewController
Merge pull request #742 from robertfausk/master

add preBindRequest($model) in indexAction of EditController and NewController
Show and excel actions do not generate forms (just like the list action) and can thus be virtual types
Merge pull request #743 from bobvandevijver/master

Excel/Show actions virtual types