Code clean up

- CommandHelper:performCommand() now returns the output of the command and only log it in debug mode
- Cleaned up all top-level try-catch statements
- Replace "/" with File.separator
Added new goal 'update-version'

- Took out versioning from the 'build' goal
- Added new execution goal 'update-version'. You can either specify the build number or let the plugin auto-increment it
Added support for CocoaPods

During 'build' goal execution the plugin will check if the working directory contains a Podfile and will automatically try to update the pods.
You can disable that by setting 'updatePods' to 'false'.
Added support for specifying the target to build

The 'goal' build will try to compile the project using the 'target' parameter only if no scheme was specified.