Multiple updates

## Ready State: Yes

* Updated .gitignore file to contain `.rej` file extensions.
* Added LICENSE.md file.
* Added file header comments with appropriate licensing information.
* Updated UUID Menu Links module version to 0.4.1.
* Moved files located within `includes/install` to just `includes`.
* Added ImagexInstallKitInstallCallbackTask installation task handler.
* Added install operation keys and respective constants.
* Moved away from relying on Drupal core's install profile modules task operation as a bootstrap for creating module list and operations, instead implemented own version (assists with install performance).
* Added `uuid_menu_links_sync` if module exists as part of default tasks.
* Added `hook_imagex_installkit_install_profile_modules` hook.
* Added `imagex_installkit_profile_alter()` callback, similar to `drupal_alter` but for profiles during installation.
* Added exception logging for any Exceptions caught during task execution in `try { } catch { }`.