POM: bump to pom-imagej 5.0

This restructures the parent POM dependency management,
and inherits the latest dependency versions.
HobbesUploader: work around bugs in SJC

Specifically, version 2.35.0 of scijava-common has a bug where
getTitle() returns null if the plugin is Identifiable but the class
cannot be loaded for some reason (i.e., because loadClass() returns
null). That bug is fixed with the following commit:

https://github.com/scijava/scijava-common/commit/93c340f472401567dee50f2edbb70abbff261749

However, to avoid the test failure before that fix gets released,
let's avoid the issue by giving the HobbesUploader a specific name,
which will be returned by getTitle() before the identifier is even
checked.

As an aside: while getTitle() is never supposed to return null, it still
wouldn't be an issue if the AbstractUIDetails#compareTo method were more
tolerant of null titles. That fix was also committed:

https://github.com/scijava/scijava-common/commit/bce7b69391791f39b5019dca14bf110816c97265
POM: tweak whitespace

This makes the tidy-maven-plugin happier.
POM: declare main class as a property

This lets us reuse the pom-scijava ancestor's exec profile:

    mvn -Pexec
CommandLine: don't pass null to System.setProperty

At least on my platform (OS X 10.10 with Apple Java 1.6.0_65),
trying to assign a null value to a key via System.setProperty
results in an exception:

Exception in thread "main" java.lang.NullPointerException
	at java.util.Hashtable.put(Hashtable.java:394)
	at java.util.Properties.setProperty(Properties.java:143)
	at java.lang.System.setProperty(System.java:745)
	at net.imagej.updater.CommandLine.main(CommandLine.java:1366)

So let's guard against that possibility, only assigning non-null values.