[Decoder] Add bounding box plugin

[Decoder] Add bounding box plugin

1. The basic mechanism is imported from nnstreamer_example/example_object_detection.
2. The mechanism is updated to support
    - Different tensor types (it supports integers and double as well if the two tensors have the same type)
    - Input tensors may have smaller number of detections (less than DETECTION_MAX)
    - A few performance updates to execute less loops
3. No more dependencies on graphics library for drawing boxes or rendering text
4. Imported "font.c" of Silicon Graphics Inc 1992 to render text. The license is open for any purpose as long as the license statement is in tact.
5. Tested with a basic case
```
gst-launch-1.0 --gst-debug=2  \
        v4l2src name=cam_src ! videoscale ! videoconvert ! video/x-raw,width=640,height=480,format=RGB,framerate=30/1 ! tee name=t \
        t. ! queue leaky=2 max-size-buffers=2 ! videoscale ! video/x-raw,width=300,height=300,format=RGB ! tensor_converter ! \
                tensor_transform mode=arithmetic option=typecast:float32,add:-127,mul:0.007843 ! \
                tensor_filter framework=tensorflow-lite model=ssd_mobilenet_v2_coco.tflite ! \
                tensor_decoder mode=bounding_boxes option1=ssd option2=coco_labels_list.txt option3=box_priors.txt option4=640:480 option5=300:300 ! \
                compositor name=mix sink_0::zorder=2 sink_1::zorder=1 ! videoconvert ! ximagesink \
        t. ! queue leaky=2 max-size-buffers=10 ! mix.
```

In later PRs, we need
- Test cases (and probably some fixes)
- Hardcode the pre-processing results of font.h, then remove the "rasters" from font.h

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>