added generic configuration checking for inputs, instead of doing it manually in every subclass

remove checkConfiguration(Configuration) method and replaced it with setConfiguration(config) + checkConfiguration() to maintain sanity
include dropdown fields in configuration checks
Only use self-signed TLS cert/key if TLS is enabled
Remove obsolete ObjectMapper from RestApiService
honor default buffer receive size config file parameter when setting default value for interface
remove unused constant
Improve readability and completeness of PrintModelProcessor output

The previous implementation of PrintModelProcessor didn't output all registered
resources from the Jersey ResourceModel. The output is now complete, sorted and
printed through the logging subsystem instead of being dumped to stdout.
Adding maven set version backups to gitignore
Merge branch 'master' of github.com:Graylog2/graylog2-server
Fix resource filtering for graylog2-radio
Mask passwords in output configuration to avoid showing them in web.

This is just a quick & dirty fix. See #742 for a follow up issue.

Fixes #740.
Not pausing queue-based inputs for all Lifecycles != RUNNING.

Before this, queue-based inputs were paused for all lifecycle states
beside RUNNING. This would prevent any processing for lb:override states
which are independent of the message processing state.
Replace custom plugin loader with Java ServiceLoader

The previously used mechanism for loading plugins into Graylog2 was reimplementing
the functionality provided by the standard Java [ServiceLoader][1] facility.

Plugin authors can now bundle multiple plugins in one single JAR artifact. Instead
of creating a graylog2-plugin.properties file, plugin authors have to create a
file named META-INF/services/org.graylog2.plugin.Plugin which contains a list of
classes implementing the Plugin interface (one FQCN per line).

[1]: http://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html