CB-5885 Allow simultaneous install/uninstall of multiple plugins

This PR allows plugman to install or uninstall a list of plugins with one invocation. This speeds up the installation of 20 plugins with about 20 to 50% and that of 5 plugins with up to 100%. The list is specified by repeating the --plugin <url, path, id> option as many times as needed.

<b>Update:</b> Added a simple cache in the <b>ios.parseProjectFile</b> function. This additionally speeds up the installation of ios plugins several times depending on the complexity of the project.

https://issues.apache.org/jira/browse/CB-5885