add a tag property to window, allow update tag with dispatch, and match with tag

[rtgiskard]

Description

Currently windowrule only match with limitted fields, which can't be modified by the user with convenience, if every window has a list of tags, and there is a dispatcher to manipulate (add/delete tag) it, and windowrule is able to match with tags, then user will be able to do many things, for example:

1. adjust opacity of a specific window with keybindings on the fly
2. mark windows in any workspace, and operate with the marks