Currentscape

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Fixed
~~~~~
- Test data in test_currentscape_functions.

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Fixed
~~~~~
- Unit conversion when turning current density into currents in extract_currs.

Added
~~~~~
- Added tests for data processing functions.
- Added warning when there is not enough colors in colormap.

Changes
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- Refactored currentscape into smaller, more meaningful modules.
- Changed default left-side adjusting,
so that the labels and ticks do not overlap.
- Changed dict key for blackline thickness and x-chunksize in config
since they should not belong exclusively to currentscape anymore.
- Changed 'labels' and 'ticklabels' to 'ylabels' and 'yticklabels' in config["show"]
to distinguish them from 'xlabels' and 'xticklabels'.

New Features
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- Reorder the currents in each subplot,
so that the currents with the largest contribution lay at the top.
The legend is reordered accordingly.
- Added an autoscaling for y limits and ticks for current (and ions) subplots.
- Added a new subplot to currentscape: absolute currents.
- Absolute currents can be displayed as lines or as a stackplot.
- Allowed extract_currs to extract ionic concentration.
- Added a new subplot to currentscape: ionic concentration.
- Added a new subplot: pie charts showing the overall contribution of currents.
- Label and ticklabel of the x axis can now be displayed on the bottom plot.
- Gridlines corresponding to the x ticks can be displayed on all the plots.
- x ticks can be custom or generated automatically.
- Currentscape plotting can be disabled in the config.

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Fixes
~~~~~
- Currentscape used to fill empty data (e.g. no inward/outward current at all)
with the first color in data. Now it fills it with white.
- Fixed config example in README and doc.
- Removed top and bottom frame of currentscape which was hiding part of the data.
- Fixed central black line separating currentscape plots that weas hiding part of the data.

New Features
~~~~~~~~~~~~
- Added new colormap choices.
- Added possibility of putting patterns (hatches) on top of color palette.
- When using patterns, matplotlib uses bar plots, which takes some time to compute,
so reducing x-resolution was enabled.
- Chunksize (when reducing x-resolution) is corrected when not a divisor of data size.
- Patterns color, design and 'density' can be customised.
- The legend y position can be customised.
- Added a 'mixer' that prevent two successive currents to have the same color or pattern.
- Added library to easily extract currents from any location (soma or other).
- Now uses neuron in extract_currs lib to get the segment area and use it to turn
current densities into currents.
- Can use default protocols from singlecell-optimization, or custom protocols.
- Added tests for extract currents.

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- Added docs to tox envlist.

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Fixes
~~~~~
- Fixed non pylint-conform style.

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New Features
~~~~~~~~~~~~
- Added documentation.