Improve message for no level key

[naoliv]

With indoorhelper installed we see a warning for basically everything in our dataset, saying This object has no level tag., use Delete the object or use the plug-in to add a POI tag! instead

The message (1) and/or the test (2) should probably be reviewed to:

(1) avoid people wrongly deleting objects
(2) avoid a warning for every way without level

JOSM:

Revision:14449
Is-Local-Build:true
Build-Date:2018-11-25 12:22:37

Identification: JOSM/1.5 (14449 SVN pt_BR) Linux Debian GNU/Linux unstable (sid)
Memory Usage: 973 MB / 2048 MB (128 MB allocated, but free)
Java version: 11.0.1+13-Debian-2, Oracle Corporation, OpenJDK 64-Bit Server VM
Screen: :0.0 1920x1080
Maximum Screen Size: 1920x1080
Java package: openjdk-11-jre:amd64-11.0.1+13-2
Java ATK Wrapper package: libatk-wrapper-java:all-0.33.3-21
VM arguments: [-Dawt.useSystemAAFontSettings=gasp]
Dataset consistency test: No problems found

Plugins:
+ BuildingGeneralization (23)
+ ImportImagePlugin (34576)
+ OpeningHoursEditor (34535)
+ SimplifyArea (34586)
+ apache-commons (34506)
+ buildings_tools (34724)
+ download_along (34503)
+ editgpx (34737)
+ ejml (34389)
+ geojson (87)
+ geotools (34513)
+ indoorhelper (34734)
+ jaxb (34506)
+ jogl (1.2.2)
+ jts (34524)
+ log4j (34527)
+ measurement (34529)
+ merge-overlap (34664)
+ opendata (34698)
+ poly (34546)
+ pt_assistant (2.1.10)
+ reverter (34552)
+ tageditor (34560)
+ todo (30306)
+ turnlanes-tagging (272)
+ turnrestrictions (34643)
+ undelete (34568)
+ utilsplugin2 (34506)
+ wikipedia (v1.1.1)

[Don-vip]

Fixed in [o34739:34740].