refactor plugin_manager using symfony/console, refs #122

cli/commands/AbstractPluginCommand.php

cli/commands/PluginActivate.php

cli/commands/PluginDeactivate.php

cli/commands/PluginInfo.php

cli/commands/PluginInstall.php

cli/commands/PluginListMigrations.php

cli/commands/PluginMigrate.php

cli/commands/PluginRegister.php

cli/commands/PluginScan.php

cli/commands/PluginUnregister.php

cli/getopts.php

cli/studip

composer.json

composer.lock