[FEATURE] General cache location for stadium image in Area Sizer

[sgcr]

Is your feature request related to a problem? Please describe.
As described in #2409 there is the need for a cache mechanism of the stadium image.

Describe the solution you'd like
The idea is provide a cache that is valid for 24 hours after the last download for a specific URL, so that the traffic to Hattrick on each start of the program when the Arena Sizer is used.

Additional context
The question is where the cache should be and shall be discussed in that issue.
I see these two options:

• users home directory: I saw System.getProperty("user.home") + "/.ho" for Linux, System.getProperty("user.home") + "/Library/Application Support/HO" for Mac and System.getenv("AppData") + "/HO" for everything else which means Windows effectively.
• database: which means we have a table with rows and columns that provides the data

[wsbrenk]

I don't think that invalidation of the image after 24 hours is a good idea. My stadium pictures will never change. We should handle it the same way as the team logos are handled. I would store them on the local disk. Maybe you add a update option, when user wants to download a new picture of his stadium.

[sgcr]

@wsbrenk

I've created PR #2457 with a local cache for stadium images. The cache location is provided by the ThemeManager.

There is currently no cache invalidation implemented, following the previous discussion.

I think this works as a first step. However, from a user perspective, a simple TTL-based invalidation might still be useful. The image is not downloaded on every program start anyway, but only when the Arena Sizer dialog is opened. So even with a 24h TTL, the additional traffic should stay very limited, while avoiding permanently stale cached images.

With such a TTL-based approach, an explicit reload button would probably not be necessary.