6 mtc4bt large controller configjson files crash the controller at start up

[raymondbrink]

Moved away from StaticJsonDocument (on the stack) to DynamicJsonDocument (on the heap).

You can now put each loco config into a separate file (max. 4k):

You can even combine loco config files with inline loco configurations (for backwards compatibility):

[Mattzobricks]

Tested, works fine.

[Mattzobricks]

Let's merge it into develop, not master.

[raymondbrink]

I rebased this feature onto develop, so it now includes the latest changes for PU hub onboard LED control.

[Mattzobricks]

Very nice, thank you.