Release 1.5.2

• further work on synchronization to avoid deadlocks (see https://josm.openstreetmap.de/ticket/14638)
• fix NullPointerException when trying to "jump to blue" (see https://josm.openstreetmap.de/ticket/12742)
• fix IllegalComponentStateException when the plugin wants to show a ImageInfoHelpPopup (see #48 and https://josm.openstreetmap.de/ticket/14627)
• caches are all moved to a centralized class
• more test coverage

Note: This release contains a bug, which prevents the plugin from downloading the thumbnails for the Mapillary images (see #48 (comment)). All users are recommended to upgrade to v1.5.3, which is completely the same except it also includes a fix for the aforementioned issue.