Fix Sphinx documentation issues.

[ianhelle]

Several of the notebooks and modules are not being included in the RTD information because either:

• there is an import error in the module
• the document hasn't been included in the ToC/parent documents

Additionally we need to implement the same changes as msticpy to mock packages
such as sklearn and matplotlib

[ianhelle]

Sphinx build

---------------------------------------------------------------------
MsticpyImportExtraError - Error importing Scikit Learn and matplotlib
---------------------------------------------------------------------
Cannot use this feature without Sklearn and matplotlib installed
This feature requires one or more additional packages to be installed.
To do this run the command:
pip install msticpy[ml]

For more help on fixing this error see:
 - Installing msticpy

Exception context:
Stack:
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module

  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/analysis/eventcluster.py", line 56, in <module>
    extra="ml",

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/common/exceptions.py", line 436, in __init__
    super().__init__(*add_args, help_uri=uri, **kwargs)

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/common/exceptions.py", line 119, in __init__
    stack=traceback.format_stack(limit=5),

---
Locals:
self (MsticpyImportExtraError) = Cannot use this feature without Sklearn and matplotlib installed
help_uri (NoneType) = None
args (tuple) = ('Cannot use this feature without Sklearn and matplotlib installed',)
kwargs (dict) = {'title': 'Error importing Scikit Learn and matplotlib'}
extra (str) = ml
mssg (str) = This feature requires one or more additional packages to be installed.
To do this run the command:
pip install msticpy[ml]
add_args (list) = ['Cannot use this feature without Sklearn and matplotlib installed', 'This feature requires one or more additional packages to be installed.\nTo do this run the command:\npip install msticpy[ml]']
uri (tuple) = ('Installing msticpy', 'https://msticpy.readthedocs.io/en/latest/getting_started/Installing.html')
__class__ (type) = <class 'msticpy.common.exceptions.MsticpyImportExtraError'>
---
Exception was raised by:
Traceback (most recent call last):

  File "/home/docs/checkouts/readthedocs.org/user_builds/msticnb/envs/stable/lib/python3.7/site-packages/msticpy/analysis/eventcluster.py", line 48, in <module>
    from sklearn.cluster import DBSCAN

ModuleNotFoundError: No module named 'sklearn'

Note missing notebooklets

looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [  4%] creatingnotebooklets
writing output... [  9%] index
writing output... [ 13%] msticnb
writing output... [ 18%] msticnb.nb
writing output... [ 22%] msticnb.nb.azsent
writing output... [ 27%] msticnb.nb.azsent.account
writing output... [ 31%] msticnb.nb.azsent.alert
writing output... [ 36%] msticnb.nb.azsent.host
writing output... [ 40%] msticnb.nb.azsent.network
writing output... [ 45%] msticnb.nb.template
writing output... [ 50%] msticnb.nblib
writing output... [ 54%] msticnb.nblib.azsent
writing output... [ 59%] nb_doc_details
writing output... [ 63%] notebooklet_docs/AccountSummary
writing output... [ 68%] notebooklet_docs/EnrichAlerts
writing output... [ 72%] notebooklet_docs/HostLogonsSummary
writing output... [ 77%] notebooklet_docs/HostSummary
writing output... [ 81%] notebooklet_docs/IpAddressSummary
writing output... [ 86%] notebooklet_docs/LogonSessionsRarity
writing output... [ 90%] notebooklet_docs/NetworkFlowSummary
writing output... [ 95%] notebooklet_docs/WinHostEvents
writing output... [100%] notebooklets_summary