Added a simple Python GUI app for playing videos

This app is inspired by the examples/pvr.py (which itself is based on
existing examples in Python bindings) but is much simpler and completely
rewritten to support GStreamer-1.0 and GObject introspection (manually
written bindings for GStreamer are no londger supported).

It's main purpose is to test the timeshifter element. Currently it plays by
default (no arguments) a pipeline which receives raw TS over UDP on port
10000.
If an HTTP URL is given on the command line as an argument, it will play
the pointed asset instead.
Fix whitespace
Remove support for Gstreamer 1.0
Using GstFileMemAllocator to allocate memory for slots

The work on GstFileMemAllocator that uses mmap() to extend physical memory
available is available here:
https://github.com/kkonopko/gstreamer/tree/filemem-allocator
Fixed issue with buffer references

The ringbuffer holds a list of buffers used as memory containers (slots).
When a buffer is sent dowstream, it's actually supposed to be consumed and
disposed. To avoid that and reuse buffers need to copy them before sending
them downstream. The copy is a "shallow" copy though so the actual memory
is shared.
Minor patch for the dump_cache_state()

The state string LUT should have items reordered.
Removed all recording related code

Removing should be decoupled anyway and handled by a separate element.
Having this feature in the timeshifter itself only complicates it.

Now we are in a better position to test and improve it.

Other:
- fixed a regression: buffer metadata was not added so when buffer was
  consumed, the slot did not change its state from POP to RECYCLE (this is
  handled in metadata "dectructor": gst_slot_meta_free()

- returning gboolean from gst_shifter_cache_push as we need to indicate
  overrun situation

- renamed/removed any "recording" related entities to "temp" related to
  avoid confusion (recording is not intended to be an integral part of the
  timeshifter)
Fixed a regression: slots not recycled

Buffer metadata was not added so when a buffer was consumed, the slot did
not change its state from POP to RECYCLE (this is handled in metadata
"dectructor": gst_slot_meta_free())