Always launch the app post install if already up to date. Fixes #69

This maintains existing behaviour unless both isInitialInstall and firstRunOnly (now renamed to runOnly) are true, which only happens if no release was selected for install.

Previously, given those parameters, invokePostInstall would create shortcuts for non-squirrel-aware applications, then return. Now in addition to creating said shortcuts, it will run the application, which appears to be the intended behaviour.

This makes rerunning the installer start the installed application again after ebb6bb2c5a4c9d05f0abaaff99efe904f7232f4d