This PR proposes 4 related enhancements that brings some recent changes in StimulusReflex full circle.

1. The dom_id function has been moved to CableReady::Identifiable, which we will include in StimulusReflex's reflex.rb class as a way to consolidate one implementation of the function. Also, users can include this module in their own projects.
2. CableReady selectors can now accept ActiveRecord::Base and ActiveRecord::Relation objects, the same way the new StimulusReflex morph method accepts them eg. implicit dom_id for morph selectors stimulus_reflex#436
3. When adding an operation, the method now accepts an optional selector as a first parameter. This is a shortcut since so many operations accept a selector, and saves the developer from having to type selector: "#users". If a selector is provided in the options, it overrides a specified selector.
4. Each CableReady channel now remembers the selector from the previous operation, if any. This means that you can specify a selector at the beginning of a chain, and it will automatically be picked up by succeeding operations until a new selector is used, at which point that becomes the "new previous" operation for all following operations; if a new selector is used, all previously used selectors are unmodifed.

include CableReady::Identifiable

puts dom_id(User.all, :happy) # "#happy_users"
puts dom_id(User.first) # "#user_1"

cable_ready.inner_html(selector: User.first, html: "<span>Your mother</span>")

cable_ready.inner_html("#smelly", html: "<b>All hype</b>")
cable_ready.inner_html(User.all, html: "<i>mmm</i>")

cable_ready.set_focus("#smelly").inner_html(html: "<span>I rock</span>").set_style(name: "color", value: "red").text_content(selector: User.all, text: "Bloom")