- fixed bug period range generation

- started splitting the Home controller in the plugins controllers
- now no need to create a controller.php you can put all the classes in one plugin file
- developped the plugin administration screen
- added activate/desactivate plugins/ saved in config file / added config file write
- redone menu generation. now plugins can create menu entries level1 or level2
- fixed wronte row id in sitemanager when adding a site

git-svn-id: http://dev.piwik.org/svn/trunk@254 59fd770c-687e-43c8-a1e3-f5a4ff64c105