Reference field common tasks

[borsi]

Tasks:

• [x] My nice silky Loading
  • [x] The main control needs to know what to load
• [x] Mapping extension for the reference field
• [x] Search in references in client-js
• [x] Weave it through the redux layer

[gallayl]

Search in references

• [x] Create a query expression based on a search string, allowed types (Type) and selection roots(InTree)
• related to https://github.com/SenseNet/sn-client-js/issues/38