Allow per-map setting of imagery.generic.*_expires

[jidanni]

Please allow per-map setting of imagery.generic.*_expires.

Otherwise even if just one map on one site needs a different setting,
not only all the maps on that site are forced to use it,
every map on every site is too.

Compare
​http://www.offline-maps.net/en/help/maps/stored/custom#advanced_example 's
per-map <update-delay> tag.

[jidanni]

​http://www.alpinequest.net/en/help/v2/maps/on-demand-create has even more features.

[jidanni]

P.S., imagery.generic.minimum_expires has no documentation yet.
When creating the documentation do mention how it interacts with the tags servers send. E.g., as seen in
​https://help.openstreetmap.org/questions/62203/how-to-change-josm-imagerygenericminimum_expires-but-just-for-one-imagery
Say if it overrides those tags and which.

[Don-vip]

For future reference:

/**
 * Class bridging TMS requests to JCS cache requests
 *
 * @author Wiktor Niesiobędzki
 * @since 8168
 */
public class TMSCachedTileLoaderJob extends JCSCachedTileLoaderJob<String, BufferedImageCacheEntry> implements TileJob, ICachedLoaderListener {
    private static final LongProperty MAXIMUM_EXPIRES = new LongProperty("imagery.generic.maximum_expires", TimeUnit.DAYS.toMillis(30));
    private static final LongProperty MINIMUM_EXPIRES = new LongProperty("imagery.generic.minimum_expires", TimeUnit.HOURS.toMillis(1));

[simon04]

Setting a custom minimumTileExpire for one imagery entry is already possible thanks to r13733: