Allow to select a specific workspace

[jmatsu]

Close #316

This change includes breaking changes because the current custom detection has been removed and all are delegated to Gym's auto detection. Scheme, build configuration and provisioning profiles can be resolved as the current implementation does, however, this changes asks users to choose a proper one if multiple projects and/or workspaces are found. Project/workspace detection caused many troubles because the detection wasn't chosen with accuracy.