Categories optionally configured with pairs of throttled node labels.

JENKINS-19645
Pairs make each maximum applicable to nodes with matching labels only.
- Achieved by adding such Maximum Per Labeled Node pairs to categories.
Category's Maximum Concurrent Builds Per Node is superseded if matching.
Merge pull request #7 from marco-miller/labels

Categories optionally configured with pairs of throttled node labels.
[maven-release-plugin] prepare release throttle-concurrents-1.8
[maven-release-plugin] prepare for next development iteration
Merge branch 'master' of https://github.com/jenkinsci/throttle-concurrent-builds-plugin

Conflicts:
	src/main/java/hudson/plugins/throttleconcurrents/ThrottleQueueTaskDispatcher.java

Signed-off-by: Oleg Nenashev <nenashev@synopsys.com>
Fixed imports after the merge

Signed-off-by: Oleg Nenashev <nenashev@synopsys.com>