till now when no explicit value was set on a property, the default value
for that property was returned, also if the property was not applicable
to the selected runner.
Fix this, showing default values for properties only when relevant and
showing instead -1 or null when the property is not relevant for the
selected runner.
Moreover, reset all the properties but the link-watchers when the team.runner
is changed: this is required to clean up the properties unrelated to the
new runner and start with the runner-specific defaults.