[Patch] Fix for last failing JOSM test

[mdk]

The last failing test is org.openstreetmap.josm.gui.preferences.map.TaggingPresetPreferenceTestIT.testValidityOfAvailablePresets.
The reason is that the OAM preset refers to the icons in JOSM: ​https://github.com/molysgaard/OAM-JOSM/blob/master/oam-presets.xml:

<group name="OAM" icon="styles/standard/transport/way/way_secondary.svg">
<item name="Airspace" icon="styles/standard/transport/way/way_motorway.svg" type="closedway">
<item name="Navaid" icon="styles/standard/transport/way/way_secondary.svg">
<item name="Obstacle" icon="styles/standard/transport/way/way_secondary.svg">
<item name="Aerodrome" icon="styles/standard/transport/way/way_secondary.svg" type="relation,node">
<item name="VFR Reporting Point" icon="styles/standard/transport/way/way_secondary.svg">

It looks like the icons moved in JOSM from styles/standard/ to images/presets/. Bothe icons used above still exists:

https://josm.openstreetmap.de/browser/josm/trunk/images/presets/transport/way/way_secondary.svg
https://josm.openstreetmap.de/browser/josm/trunk/images/presets/transport/way/way_motorway.svg

@Don-vip: You are the last contibutor of ​https://github.com/molysgaard/OAM-JOSM/blob/master/oam-presets.xml, so it should be easy for you to fix the icon paths in that file.

[Don-vip]

I am not the author of the style I only created a PR long ago.
Klumbumbus has already created the new PR we're waiting for its merging...

​https://github.com/molysgaard/OAM-JOSM/pull/5