MODE-1805 Query system can be disabled in AS7 kit

Added ability to completely disable the query system (including the
generation/maintenance of indexes) in a repository in the AS7
subsystem. (The JSON repository configurations had this ability for
some time, but it could not be controlled in AS7.)

This adds a new "enable-queries" XML attribute on the "repository"
element in the subsystem configuration. This attributes defaults
to "true" and therefore is backward compatible. However, setting it
to "false" will completely disable the indexing system, although
any index storage and indexing configuration within a repository
configuration will remain as-is; it will simply not be used.
This means that the repository's indexes and query system can be
disabled (perhaps on a temporary basis) and then re-enabled without
having to completely reconfigure the index storage and indexing
parameters.

It was discovered that executing queries on a repository that had
its query system disabled resulted in a NPE, because the running
state did not have a RepositoryQueryManager instance. Rather than
deal with all of the potential NPEs, a new specialization of
the RepositoryQueryManager, called RepositoryDisabledQueryManager,
was added and is instantiated within the running state when queries
are disabled. This specialization essentially no-ops all of the
operations. The result is that queries will return no results
rather than throw an exception.

Additional warning messages are logged when the indexes are indeed
disabled, since this will rarely be done in production.

Several new tests were added, including unit tests (in
'modeshape-jcr') and integration tests for the AS7 subsystem.
MODE-1805 Minor cleanup of code per code review