NFD

Implement FIB API over NameTree.

• FIB entry has a pointer to the NameTree entry with same Name.
• Fib::insert inserts a NameTree entry, and attaches fib::Entry onto NameTree entry.
• Fib::remove detaches fib::Entry from NameTree entry, but does not delete the NameTree entry.
• Fib::findLongestPrefixMatch and Fib::findExactMatch use corresponding features in NameTree API.
• Fib::removeNextHopsFromAllEntries uses NameTree enumeration API.
• Fib iterator uses NameTree enumeration API.