Plugin improvements

I restructured the UI and added some new features:

* If Keychains are unlocked during the build process, the keychains are restored to the state before the build after it completes or fails (our SSH key password was inside the login keychain and the plugin unlocked another keychain but did not restore the login keychain)

* You can define a pattern for the .ipa file name

I'm not accustomated to Java development or have any experience with Jenkins plugin development, so please feel free to make any changes to this pull request or drop it. I just wanted to share the improvements, that kept me from using the plugin for our CI environment.