workaround edvr merger with basicsr

[robvanhooren]

to workaround the edvr merger with basicsr in August 2020, specify the pre-merge git branch, thusly:

!git clone -b old_version https://github.com/xinntao/EDVR

note, the old version is no longer actively maintained.

[robvanhooren]

further notes:

• apparently, the experiments/pretrained_models dir wants to be created manually
• change all occurrences of python/pip to python3/pip3
• dcn needs to be built by hand before the develop, make the following changes to be compatible with recent versions of pytorch...

in deform_conv_cuda.cpp, change all occurrences of AT_CHECK to TORCH_CHECK

In deform_conv_cuda_kernel.cu, find all of the occurrences of data_col.data data_im.data data_mask.data data_offset.data grad_im.data grad_offset.data grad_mask.data and postfix the string "_ptr" to each. i.e. data_col.data becomes data_col.data_ptr

thenceforth, "combining everything" may continue...