[PATCH] GPX layers should use the name from the file instead of `Downloaded GPX Data` whenever possible

[taylor.smock]

Right now it is not possible to set the name of a GPX layer on download. This means that GPX layers are commonly called Download GPX Data. It would be nice, if there is a name in the metadata, if JOSM could use that instead.

Use cases:
Tasking Managers could send an XML file that looks like this:

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<gpx creator="HOT Tasking Manager" version="1.1">
<metadata>
<link href="https://github.com/hotosm/tasking-manager">
<text>HOT Tasking Manager</text>
</link>
<time>2019-12-31T21:56:28.586152</time>
<name>Tasking Manager: Project 1, Task 1</name>
</metadata>
<trk>
<name>
Task for project 1. Do not edit outside of this area!
</name>
<trkseg>
<trkpt lat="39.070328" lon="-108.561121"/>
<trkpt lat="39.070438" lon="-108.571025"/>
<trkpt lat="39.077663" lon="-108.57099"/>
<trkpt lat="39.077499" lon="-108.56091"/>
<trkpt lat="39.070328" lon="-108.561121"/>
</trkseg>
</trk>
<wpt lat="39.070328" lon="-108.561121"/>
<wpt lat="39.070438" lon="-108.571025"/>
<wpt lat="39.077663" lon="-108.57099"/>
<wpt lat="39.077499" lon="-108.56091"/>
<wpt lat="39.070328" lon="-108.561121"/>
</gpx>

Please note that the current version of the tasking manager (TM3) creates an empty layer with the desired name and then loads in the GPX file.

[taylor.smock]

Initial patch (no tests)