Add additional cache support for OkHttp

[andreynovikov]

Add cache support for OkHttp in the same format as LwHttp.

[devemux86]

Why the internal InputStream here since we already extend it?

[andreynovikov]

Because it's a kind of proxy. Do you wish to use super instead?

[devemux86]

Since we don't use internally a different InputStream type than the extended one, we could simplify the implementation?

[devemux86]

Also we could make the inner class static?

[andreynovikov]

Ok, I'll test it later.

[devemux86]

Do we need another implementation since OkHttp provides its own response cache and already exists OkHttpFactory(HttpResponseCache)?
See OkHttpEngineTest for sample example.

Reference opensciencemap#89, opensciencemap#100

[andreynovikov]

Yes, that cache caches complete HTTP responses. I've implemented the same type of cache as in LwHttp when tile image blob is cached. This:

1. Lets interchange engines.
2. Makes cache useful without HTTP at all.

[stleusc]

why would we need OkHttp cache without HTTP? And does it really make sense to think about someone changing the engine while keeping the cache? NO!
We should stay more generic and use what is there.
Use OkHttp built in caching...

Lastly, there is WAY newer version of OkHttp out there and before making changes like that we should upgrade to that.

[devemux86]

there is WAY newer version of OkHttp out there and before making changes like that we should upgrade to that.

I opened #138 for that.

[andreynovikov]

Will return to it later after #138

[devemux86]

@andreynovikov we can close this?
Need to address first #138 and any work can be posted on new vtm-http module.