Migrate **Document**Builder bloc to cubit

[damian-molinski]

Summary

In order to maximise reusability of document builder logic and UI we're going to migrate bloc to cubit and use similar approach to proposal viewer

Description

While working on this migration we're going to drop remaining old models of proposals

Models and functions to drop

• CoreProposal and it's extensions
• ProposalData, ProposalTemplateMoneyFormats, ProposalVersion, ProposalUserContext
• ProposalService.getProposal(), ProposalService.getProposalDetail()

Related PR

• feat(cat-voices): reusable document builder #4054

Related Issues

• Reusable document builder #3955
• Representative profile builder #3986