Increased minimum PHP version to 5.4.

This allows to use short array syntax and other new features.
Made request passing in ValidationEvent mandatory.

Take a look at fc2ed9a6b798c71951806c8c9ed6e1366856272e and #23
for details.
Removed default value 'fineuploader' for frontend key in Configuration.

This was a legacy decision which will be changed in 1.0.0.
The first version of this Bundle only supported Fineuploader which
would have been a BC break if 'fineuploader' would not have been
set as default.
Use array short syntax.