Match the boilerplate master & Remove TODO lines already done by Grunt

Modifications as follows:
1. Remove `TODO` lines that Grunt automatically handles
2. Remaining `TODO` lines (not automatically handled by Grunt) are marked as `@TODO`, same as the master.
3. Remove `screen_icon()` function in `root/admin/views/admin.php` as done in the master (since this function is deprecated)
4. Fixing `languages/` to `/languages/` in `load_plugin_textdomain` function in `root/public/class-plugin-name.php`, as done in the original boilerplate master.
5. Other  Small Modifications as done in the original boilerplate master.