Wrapping core's Table::get_name() method for internal use.

@bmunkholm @emanuelez @cmelchior 
You are copying the string twice here. That is not necessary.

Also, Java is using a non-standard version of UTF-8, so this can also cause you code to fail. The right thing to do here, is to use our custom string conversion function. This applies to all strings that are part of/stored in the Realm. Tables names are such strings.

Everybody working on the Java binding must pay very close attention to this UTF-8 incompatibility issue, and remember to use our custom string conversion functions **everywhere**.

@emanuelez @cmelchior