EnumConverter - try to dynamically extract enum type from ValueExpression

[tandraschko]

Currently EnumConverter requires a target class constructor param, we could get rid of it with:

1. like OmniFaces, getting the Enum Class in getAsString and remember
2. extracting from the value expression

[BalusC]

1. like OmniFaces, getting the Enum Class in getAsString and remember
2. extracting from the value expression

Totally in favor of this. I only think we should keep the c'tor for backwards compatbility and only perform the above tasks when class is unspecified (thus when default c'tor is used).