Allow users to define the time interval of DisplayIncome

[DeathFishAtEase]

In rulesmd.ini:

[AudioVisual]
DisplayIncome.Delay=15    ; integer

[SOMEBUILDING]            ; BuildingType
DisplayIncome.Delay=15    ; integer, defaults to [AudioVisual] -> DisplayIncome.Delay

Warning

Delay cannot be set to 0, this will change the delay to 1 and outputs a developer warning to log.

Log Example:
In rulesmd.ini:

[AudioVisual]
DisplayIncome.Delay=0
[NAREFN]
DisplayIncome.Delay=0
[GAREFN]
DisplayIncome.Delay=15

In debug.log:

...
[Phobos] [Developer warning] [AudioVisual] DisplayIncome.Delay is set to 0, forcing to 1.
[Phobos] [Developer warning] [NAREFN] DisplayIncome.Delay is set to 0, forcing to 1.
...

[phoboscn-bot]

To Chinese users:
This pull request has been mentioned on Phobos CN. There might be relevant details there:

致中文用户：
此拉取请求已在 Phobos CN 上被提及。那里可能有相关详细信息：

https://www.phoboscn.top/t/topic/436/1

[github-actions]

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[DeathFishAtEase]

Tested by: https://www.phoboscn.top/t/topic/436/2