feat: change detection mechanism refactor

[smalluban]

Change detection mechanism relays on DOM events. This has two significant drawbacks:

• We can only attach cache mechanism to objects that are HTML elements
• DOM events API is slow and complicates observing children factory due to listening bubbling event

This PR introduces a new change detection mechanism:

• It's based on internal emitter
• Allows observing changes in other properties like it was implemented in render factory (scheduler)
• Decauples cache from HTML elements - allows creating store factory with objects related to HTML elements with a proper cache mechanism connected between them

From now, instead of using @invalidate event, you have to use the observe method of the descriptor:

MyElement = {
  property: {
    get(host, lastValue) {...},
    set(host, value) {...},
    observe(host, value, lastValue) {
       // call side effects here when property value changes
    },
};

Breaking Changes

• Use observe method instead of addEventListener('@invaldiate', ...)

[coveralls]

Coverage remained the same at 100.0% when pulling d88e040 on observer-refactor into 0a3e279 on master.