Default portlet name

- Default portlet name updated from simple "SLOCCount" to "SLOCCount Statistics" to match other plugins.
[JENKINS-21552] Configureable Graph

- The graph on the job page of old projects will be nearly uninterpretable, because there are too many builds.
- Option to limit maximum number of last successful builds displayed in the graph added to the advanced configuration.
- If the value is one or less (at least two builds are required to display the graph) the number will be considered as unlimited.
- If the value is not configured, Java will interpret it as zero (unlimited), which is fully backward compatible.