Add ability to see the reason/source for several statuses/commands

[otterdahl]

For instance, reason for plan change, dark mode, yellow flash, and so forth.

The reason for changing of signal plan could be timetable, command, etc.

[emiltin]

i prefer 'source' over 'reason'.

[otterdahl]

The suggestion is to add a "return value", called "source" to the following statuses:

• S0007 Controller switched on
• S0008 Manual control
• S0009 Fixed time control
• S0010 Isolated control
• S0011 Yellow flash
• S0012 All red
• S0014 Current time plan
• S0015 Current traffic situation

"Source" is a text field which contain the reason for the new status, e.g. "operator panel", "calendar clock", "control block", "forced" etc. The exact format is not specifed.

Since we just add a return value to each status, this addition is considered to be backwards compatible. The supervision system will not recieve this value unless it is requested.

[otterdahl]

On second though, use a predefined list of reasons for the new status