Fixed code for elliptics proxy:

- removed extra headers and source files
- proxy.hpp is external header of elliptics-fastcgi
- fixed build-depends
- added data_container class to elliptics-fastcgi (hpp is external)
- added lookup_result class to elliptics-fastcgi (hpp is external)
- `bulk-upload` handler was renamed to `bulk-write`
- proxy_t was placed into namespace `elliptics`
- added enums `SUCCESS_COPIES_NUM` and `tag_user_flags` from libelliptics_proxy
Version up to 2.0.1