Add helper decorator to preserve shape of input image

[BloodAxe]

Fixes #104

Important notice
Although this PR fixes reported issue, it's kinda introduces a breaking change. So I think it's a good idea to include a 'Breaking changes' section in a release notes for next release:

• Shape of input tensors will be not changes as long as it's not required by transformation itself (Dummy dimensions will not be squeezed).

[ternaus]

👍

[albu]

Does it do nothing if shape is already fine? It's important to check this to not degrade speed.

[BloodAxe]

Reshape operation does not move memory, so it's a zero-cost op. Benchmarks on mine PC (keras commented for purpose)

                 albumentations imgaug torchvision keras
RandomCrop64             951791      -       89839     -
PadToSize512               7447      -         466     -
HorizontalFlip             1691   1292        7780     -
VerticalFlip              16789   5490       11992     -
Rotate                     1632   1013         273     -
ShiftScaleRotate           2812   1338         232     -
Brightness                  354    331         681     -
ShiftHSV                    252    148          92     -
ShiftRGB                    415    407           -     -
Gamma                      1465      -        2100     -
Grayscale                  2204    520        1370     -