enabling padding

[dkazanc]

#103
Automation of padding is required for 3D methods to work smoothly in httomo

• Auto calculation of padding based on the parameters of the method
• Enabling padding to be an attribute for every section based on which the data in blocks AND chunks will be padded
• Enable padding to work for the serial run
• Enable padding to work for the parallel run
• Adding tests for padding

[dkazanc]

OK, so the serial padding seems to work as expected. I worked with the median filter, but in principle it can be enabled with more memory hungry methods like FBP in order to check the slicing is performed correctly for every block. It is nice to see that the boundary effects on blocks disappear as the padding applied (look for the horizontal line).

[dkazanc]

the parallel run doesn't work, but not because of how padding implemented for blocks, It is how unpadding is performed (or not) for chunks. It doesn't seem to crop the padded chunks at all after padding them by looking at the dimensions. This all needs to be checked.

[dkazanc]

closing this PR as the development moved to other branches.