Update Metrics to 3.0.1

Formerly at 3.0.0-BETA3

This commit also deletes the ${metrics.version} property from the
top-level pom.  This property doesn't seem to be used anymore, and the
properties ${metrics3.version} and ${metrics2.version} are preferred
regardless to avoid confusion about which major version is implied
(Titan depends on both, 3 directly, 2 indirectly).
Fix broken unchecked cast of Number config opts

Apache Commons Config's properties file implementation seems to return
objects of type String even for small numbers that could fit in an
Integer.  In contrast, in-memory ACC configuration implementations
like those used in unit testing seem to store and return actual
numeric types (like Integer).  This commit changes
CommonsConfiguration.get(String, Class) to try to handle either case
gracefully when retrieving a value of type Number or a subtype of
Number.

Line from my config that triggered the bug:

metrics.slf4j.interval=5000

Precondition failure that appeared during execution of `g =
TitanFactory.open('path/to/config.properties')` in gremlin shell:

Invalid class for configuration value [titan.metrics.console.interval]. Expected [class java.lang.Long] but given [class java.lang.String]
Display stack trace? [yN] y
java.lang.IllegalArgumentException: Invalid class for configuration value [titan.metrics.console.interval]. Expected [class java.lang.Long] but given [class java.lang.String]
        at com.google.common.base.Preconditions.checkArgument(Preconditions.java:119)
        at com.thinkaurelius.titan.diskstorage.configuration.ConfigOption.verify(ConfigOption.java:99)
        at com.thinkaurelius.titan.diskstorage.configuration.ConfigOption.get(ConfigOption.java:93)
        at com.thinkaurelius.titan.diskstorage.configuration.MixedConfiguration.get(MixedConfiguration.java:44)
        at com.thinkaurelius.titan.graphdb.configuration.GraphDatabaseConfiguration.configureMetricsConsoleReporter(GraphDatabaseConfiguration.java:1170)
        at com.thinkaurelius.titan.graphdb.configuration.GraphDatabaseConfiguration.configureMetrics(GraphDatabaseConfiguration.java:1160)
        at com.thinkaurelius.titan.graphdb.configuration.GraphDatabaseConfiguration.preLoadConfiguration(GraphDatabaseConfiguration.java:1146)
        at com.thinkaurelius.titan.graphdb.configuration.GraphDatabaseConfiguration.<init>(GraphDatabaseConfiguration.java:1102)
        at com.thinkaurelius.titan.core.TitanFactory.open(TitanFactory.java:70)
        at com.thinkaurelius.titan.core.TitanFactory.open(TitanFactory.java:47)

I attached a debugger to check that the object on the affected line
was actually of type String before making these changes.