Localize new toolOrder.xml group names

The new toolOrder.xml file supported by SAK-16600 defines two system tool groups, which have the following defaults and can be over-ridden with definitions in sakai.properties

config.sitemanage.externalToolGroupName=Plugin Tools
config.sitemanage.ungroupedToolGroupName=Not Grouped

These properties are not localized, and should be replaced with a key/value pairing which is localized in tools.properties (where other tool groups are defined/localized). So remove the above two properties from sakai.properties, and support the following in tools.properties:

systoolgroups.lti.title = Plugin Tools
systoolgroups.ungrouped.title = Not Grouped