Custom component developers need own resource bundle

[asfimport]

Mike Stover (Bug 29603):
Anyone writing a custom jmeter component has to make resource strings. With
TestBean, it's easy enough, but for regular gui components, their only current
option is modding the messages.properties file and recompiling JMeter.

External developers should have the option of specifying a custom resource
file/location that jmeter tries to get properties from first, and then fall back
on the given jmeter resources. This would also allow anyone to override the
messages.

Version: Nightly
OS: other

[asfimport]

Sebb (migrated from Bugzilla):
Gui components can override "getStaticLabel()" to retrieve the message from a private resources file.

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@pmouawad (migrated from Bugzilla):
This bug has been marked as a duplicate of #2642

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Sebb (migrated from Bugzilla):
This is not the same as #2642, which is about upgrade.properties, not message.properties

[asfimport]

@pmouawad (migrated from Bugzilla):
Not really needed knowing all plugins that currently exist.