[com4FlowPy] minor Bugfix, documentation update and added feature for "forestFriciton", "forestDetrainment" and "forestFrictionLayer" model options

[ahuber-bfw]

Exact copy of PR #1071 on top of current master branch.

• had trouble with resolving conflicts rebasing https://github.com/avaframe/AvaFrame/tree/AH_com4FlowPy_improvForestFricitonDist with current master
• checked out this new branch from current master and applied changes from https://github.com/avaframe/AvaFrame/tree/AH_com4FlowPy_improvForestFricitonDist on top

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Original PR content:

• fixed minor bug in runCom4FlowPy.py that caused an unhandled exception if the workDir did not exist a priori with useCustomPaths option set to True
• updated com4FlowPy documentation (additional references, and small changes)
• new Feature/modelOption skipForestDist:
  • skipForestDist allows the definition of a length [m] along the track (calculated in X,Y,Z and not in projected distances X,Y- to account for different track inclinations) that needs to be surpassed, before added forestFriction is modeled. This affects all forestFriction related code if forestFriction, forestFrictionLayer or forestDetrainment are selected.
  • the feature allows to define an "initial acceleration distance" for GMFs that release in or directly above dense forest and should provide a mechanism to prevent potential under-estimation of GMF runouts in these cases.
  • By leaving the default value skipForestDist = 0 the prior model behavior remains unchanged.
• note: This makes the code ~ 5% to 10% slower in first tests

[fso42]

Standardtests ok

[qlty-cloud-legacy]

Code Climate has analyzed commit 02a2b1d and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 8.5% (50% is the threshold).

This pull request will bring the total coverage in the repository to 70.3%.

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