Stencil detection

[alexnick83]

This PR implements the StencilDetection transformation, which detects Maps that perform stencil operations and substitutes them with StencilNodes.

[codecov[bot]]

Codecov Report

Merging #833 (daad0c5) into master (f5ba6fe) will decrease coverage by 16.16%. The diff coverage is 29.64%.

:exclamation: Current head daad0c5 differs from pull request most recent head a177c71. Consider uploading reports for the commit a177c71 to get more accurate results

@@             Coverage Diff             @@
##           master     #833       +/-   ##
===========================================
- Coverage   73.38%   57.22%   -16.16%     
===========================================
  Files         278      243       -35     
  Lines       51723    45940     -5783     
===========================================
- Hits        37955    26289    -11666     
- Misses      13768    19651     +5883     

Impacted Files	Coverage Δ
dace/libraries/stencil/cpu.py	19.61% <0.00%> (-78.43%)	:arrow_down:
dace/libraries/stencil/intel_fpga.py	7.83% <0.00%> (+0.39%)	:arrow_up:
dace/libraries/stencil/subscript_converter.py	28.95% <0.00%> (-68.35%)	:arrow_down:
dace/libraries/stencil/_common.py	10.98% <5.88%> (-73.39%)	:arrow_down:
dace/transformation/dataflow/tasklet_fusion.py	15.70% <7.84%> (-78.00%)	:arrow_down:
dace/transformation/dataflow/stencil_detection.py	36.62% <36.62%> (ø)
dace/transformation/helpers.py	78.33% <38.89%> (-8.02%)	:arrow_down:
dace/transformation/dataflow/__init__.py	100.00% <100.00%> (ø)
dace/libraries/pblas/__init__.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dace/libraries/pblas/nodes/__init__.py	0.00% <0.00%> (-100.00%)	:arrow_down:
... and 254 more