Added okhttp and Bouncy Castle libraries back

@dicej removed two external libraries while porting Android classpath. Unfortunately they are necessary for networking. 
* okhttp (git clone https://android.googlesource.com/platform/external/okhttp/) is used for creating HTTP and HTTPS communications (for example, HttpURLConnection is based upon it)
* Bouncy Castle (https://android.googlesource.com/platform/external/bouncycastle/) is used to provide some cryptographic algorithms.

I put them back in my avian-pack repo (https://github.com/bigfatbrowncat/avian-pack) with an update of Avian makefile. Now networking seems to work well. And I want to pull this makefile to master now.

@dicej, as we agreed some time ago, I don't pull the libcore updates to your repo. Now the main libcore repo is https://github.com/bigfatbrowncat/avian-pack.android.libcore