Image caching: reduce socket timeout

Is there a way to reduce the socket timeout for downloading the images?

If an image is not available on the internet anymore, the timeout occurs approx. after 45 seconds. Due to loading all images in a rows, this is blocking and the image download process time increases a lot.

```
02-15 17:51:38.002 8647-8695/fr.gaulupeau.apps.InThePoche.debug D/OkHttp: Sending request http://static.blbla/20/370.jpg on null
02-15 17:52:23.009 8647-8695/fr.gaulupeau.apps.InThePoche.debug D/ImageCacheUtils: IOException while requesting imageURL=http://static.blbla/20/370.jpg in articleID=655
java.net.SocketTimeoutException

```

Start at ImageCacheUtils and trace how image requests configure their socket timeout, using the reported OkHttp and SocketTimeoutException logs as the entry point. Done means an unavailable image times out sooner than the current approximately 45 seconds and does not block loading all images in a row.

Written by the indexing model from the issue text.