Refactoring: Extract minimal `BaseForm` class

[alek13]

Generally it would be something like:

• [x] BaseForm
• [x] Form Factory with something like:
  • [x] ala mixins methods:
  • ~[ ] shared()~
  • [x] persona()
  • [x] for_node()
  • [x] with_tabs()
  • [x] extend() - class creation method
• [x] sub-classes for each minxin

Replace for forms:

• [x] reward chest form
• [x] trader form
• [x] clans chest