MODE-1719 AS7 subsystem should expose monitoring information via management layer

**_This pull-request is a simplification of and thus supersedes the [original pull-request](https://github.com/ModeShape/modeshape/pull/861)._**

Added to the JBoss subsystem the ability to gather metrics using the RepositoryStatistics provided by the JcrRepository.

Now creating 5 AS metrics (one for each window duration) for each repository metric. Changed the type from RepositoryStatistics to the interface RepositoryMonitor in the classes that needed the metrics. No longer logging in to the repository during MonitorService.start(). So metric runtime values will be "undefined" until the repository starts. Here are some other things of note:

Changed a spelling error in Window.PREVIOUS_52_WEEKS literal. From "previous-52-wees" to "previous-52-weeks."

Created constants in the interfaces of History, Statistics, RepositoryMonitor, and DurationActivity for empty or no values of these types. Some of these constants I moved from RepositoryStatistics. Also renamed the RepositoryStatistics implementations of these interfaces.