JSBSIM_ prefix in CMake options

[carlocorradini]

I'm submitting a ...

• bug report
• feature request
• support request => Please do not submit support request here, see note at the top of this template.

Describe the issue
At the moment, the majority of CMake's options have generic names (like BUILD_DOCS), which may conflict with those from a primary project that uses JSBSim.

What is the motivation / use case for changing the behavior?
To help identify the available JSBSim options and prevent potential conflicts, I recommend adding the JSBSIM_ prefix to all CMake options:
From BUILD_DOCS to JSBSIM_BUILD_DOCS
From BUILD_PYTHON_MODULE to JSBSIM_BUILD_PYTHON_MODULE
...