add LoadedPluginInformation class to process composer's installed.json file and pull out information about phpci plugins.
update plugin controller to display plugin information as well as composer package information.
Merge branch 'master' of https://github.com/Block8/PHPCI into plugin-discovery
rename LoadedPluginInformation to ComposerPluginInformation.
Extract interface for InstalledPluginInformation
add FilesPluginInformation class to retrieve plugins contained with a directory.
update PluginController to use PHPCI plugin directory as well as composer to get information about installed plugins.
Merge pull request #267 from meadsteve/plugin-discovery

RFC: Plugin discovery