Change normalisation default, fix bug in normalise_by_negative, adapt citations, absolute imports

[leanderweber]

Changes of this PR:

• [x] Make some Updates to the readthedocs
• [x] Update and Unify Citations in all Metrics
• [x] Update, unify, and sort all imports
• [x] Change all relative imports to absolute
• [x] Rethink star imports. Specifically, restructure helpers to distinguish internal functions and functions that should be user-accessible.
• [x] Change the normalisation_func default to normalise_by_max instead of normalise_by_negative due to the latter treating pos/neg values differently
• [x] Target some bugs within the normalisation functions and their application
• [x] Merge installation options rework (see PR #172)

[codecov-commenter]

Codecov Report

Merging #166 (9b1c1bb) into main (38dab8f) will decrease coverage by 1.45%. The diff coverage is 94.75%.

:exclamation: Current head 9b1c1bb differs from pull request most recent head 6bca39c. Consider uploading reports for the commit 6bca39c to get more accurate results

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
- Coverage   94.35%   92.89%   -1.46%     
==========================================
  Files          52       54       +2     
  Lines        2461     2647     +186     
==========================================
+ Hits         2322     2459     +137     
- Misses        139      188      +49     

Impacted Files	Coverage Δ
quantus/functions/discretise_func.py	100.00% <ø> (ø)
quantus/functions/loss_func.py	83.33% <ø> (ø)
quantus/functions/norm_func.py	100.00% <ø> (ø)
quantus/helpers/model/model_interface.py	76.92% <ø> (ø)
quantus/helpers/model/models.py	84.03% <ø> (ø)
quantus/functions/normalise_func.py	69.76% <31.57%> (ø)
...s/metrics/localisation/attribution_localisation.py	90.69% <80.00%> (ø)
quantus/metrics/localisation/auc.py	93.10% <87.50%> (ø)
quantus/metrics/localisation/pointing_game.py	90.32% <87.50%> (-0.31%)	:arrow_down:
...us/metrics/localisation/relevance_mass_accuracy.py	93.10% <87.50%> (ø)
... and 48 more

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[annahedstroem]

Almost ready! Two issues that need to be resolved before merging @leanderweber

1. circular import https://github.com/understandable-machine-intelligence-lab/Quantus/actions/runs/3266064142/jobs/5369251649#step:6:163
2. API-docs do no longer generate properly

[leanderweber]

The imports should be fixed. Was an issue with relative imports not having been replaced by absolute imports in base_batched.py

Also renamed normalized_axes to normalise_axes in merged content.

Not sure about the api docs not being generated properly. This is how it looks like for me when building the docs:

Is this not how it is supposed to look?