Get ride of the feature switches

[gotmachine]

We currently have the following feature switches (KERBALISM_FEATURES node) that define MM conditionals :

• Failures
• LifeSupport
• Science
• Radiation
• Stress

Those switches

• Aren't implemented properly in configs.
• Aren't implemented at all in code.

The amount of work required to make those switches work is huge, both in upfront config making / coding, and from a mod support perspective. Those options give basically 25 possible configurations, each of them requiring specific configs, code and balancing.
The ScienceOnly configs experience from 3.x is a clear example of why this is a dead end.

Radiation / life support / stress should be always be active. For players that don't want the effect on Kerbals, there will be difficulty settings options that allow to tweak/disable rules and their individual modifiers. That is a lot easier to implement, and would likely better answer the usual complaints.

Realistically, the only feature switches we can keep are features that are very well isolated from everything else. That mean Failures and eventually Science. Since the whole Failures feature is currently postponed (and if it is re-done, it will likely be released as a separate mod), I will get ride of the whole feature switch thing.