Proposal: versionning of arcade emulators

We must propose "LTS" version of arcade emulators.

Here is a proposal:

• each Major version of recalbox (8 here) will have a fixed emulator version for every emulator that depends on rom versions (fbneo, mame etc...)
• So all 8.0 will have two versions of fbneo : fbneo-1.0.0.2-rb8 and the current version, evolving with recalbox
• On 9.0, user will have the choice between: fbneo-1.0.0.2-rb8, fbneo-1.0.0.6-rb9 and the fbneo evolving with recalbox
• if emulators are too big to be embedded in the image, we should find a way to make them available
• the default version will always be the ̀current`