Improve overall documentation

Currently all usefull information are in CookBook. Nevertheless users still open issues and ask for information which most of the time are already in the Cookbook.

One It could be nice to guide users in the documentation. Several task can be done (not exhaustive):

• The "Welcome" page is the first that the user see: an improvement could be 3 profiles/persona. Users can be identified to one of them. For each of theses profiles we can personalize an "otb learning journey". It must answer theses two questions: For whom is the documentation ? Who will read the doc ?
• For the recipes/tutos, it could be nice to have an intro pages with the different categories. The image processing recipe could be separate in two recipe: "manage nodata" and "segmentation"
• [Edit 6/11] Add a TroubleShooting and Contribute pages in main pages. Theses subjects could be together or separate. TroubleShooting can be the FAQ page (currently located in Advanced Use section)
• Improve docker part (simple instructions like docker pull , docker images, docker run, docker ps), add exemples, actual links
• Talk about pyotb in specific page OR in Python API page. With a example of comparison between classic OTB python and pyotb.
• Examples of modular installation

Other documentation improvement:

• Remove all Mac and Monterverdi mentions (Global search should do the job)
• Update the "RAM usage" about QGis plugin page
• Clarify package decompression order in "Installation" page
• Generate the refineSensorModel doc (see #2423 )
• Detect, track and remove deadlinks in doc and in README and other "dev" docs (see #2430 )
• Improve "parallelization" page (see Guillaume E.B mails exchanges). How it works, what are the values that can change the streaming behavior (env var, GDAL extended file names etc...), what is the recommanded configuration ?