leaudio: LC3 encoder and decoder implementation.

Background: the fast MDCT (backward+forward) is implemented via the DCT-IV which
also needs a fast implementation. The initial approach of using directly the fast
DCT-IV from the fftw library has been extended by the alternative kissfft library.
The main purpose of using the kissfft library is a more simple integration into android.
Particularly with respect to license issues. On the other hand we needed to brake down
the DCT-IV into calling a complex fft, because the kissfft does not provide a specific
optimization for the DCT-IV. The approach via kissfft is now the default DCT-IV implementation.
It is self-contained within the lc3 module since the kissfft sources have been added completely.
There are no changes of the kissfft sources compared to the original library. The sources are taken from:

Bug: 150670922
Tag: #feature
Test: manual
Sponsor: jpawlowski@

Change-Id: I3bf6ca6e83b52ec1b70f091fb12d27744eff1424