Rewrite subtitles downloading framework

The scope of this project is to rewrite the subtitles downloading framework, in order to:
- be able to support more subtitles providers both with or without an API.
- limit requested subtitles to selected languages only instead of flooding the table with unwanted languages. 
- prioritize subtitles for hearing impaired where indicated
- provide a framework to automatically search and download subtitles at the beginning of playback without user interaction by ranking the subtitles served by each provider, based on file name information, hearing impaired and language.
- finally provide a framework to enable subtitles uploads to providers.

_Status of project:_
- [x] implement framework to support subtitles providers both with or without an API.
- [x] migrate OpenSubtitles ISDB protocol to XML-RPC protocol which supports uploads.
- [ ] implement uploading to OpenSubtitles
- [x] implement search/download/upload support for SubDB
- [x] limit requested subtitles to selected languages only instead of flooding the table with unwanted languages. 
- [x] prioritize subtitles for hearing impaired where indicated
- [x] automatically search and download subtitles at the beginning of playback without user interaction
- [ ] ranking of subtitles served by each provider, based on file name information, hearing impaired and language.
- [ ] UI settings to enable/disable subtitles providers and show info about each provider

![image](https://f.cloud.github.com/assets/5904989/1795933/cb6ee29a-6a44-11e3-8553-a9dcfe6e50ce.png)

![image](https://f.cloud.github.com/assets/5904989/1795937/ebb861fc-6a44-11e3-8ea1-94a7fef2c989.png)


Dependencies included in PR:
- [x] TimXmlRpc
- [x] minizip (part of zlib)