feat(uip-editor): store editor state (POC)

[fshovchko]

Closes: #617

[ala-n]

There is a mixed responsibility issue in the current implementation:
UIPEditor is not a state-holder and should not interact with storage/modal (the actual state-holder) unless it's directly connected with user interaction.
Consider rework of EditorStore integration considering the following points:

1. It should observe UIPModel directly or be integrated inside model and core
   1.2) Just in case there is a possibility to observe the actual initiator of change inside the core.
2. Please be aware, that the initial state depends on setting it up inside the core. The editor store is only one of the sources, there is also an anchor and default snippet used as a source. The new logic should be in sync with them in terms of priority and execution time. The UIP should not be affected by extra update events as well.