Fix Brand and Owner public links (missing / would get a 404 on brand/ and owner/)

Also follow the same URL scheme as admin (which always have trailing
slash)
Fix bug with double owner_cd in URL to owner detail
Add model BrandProposal
Add new dump, remove old ones, change dump naming, modify README

It is more useful to have a dump name match a migration name than a
date. Date can be obtained by using git blame
Add brand proposal form with placeholder template
Add redirect on BrandProposed
Fix BrandProposalForm to use BrandType in a choice
Fix status validator (MinValue = 1)
Actually create BrandProposal on submit, fix upload logo
Add user field in BrandProposal
Add user in BrandProposal
Merge pull request #51 from FrancoisDupayrat/master

Add possibility for a user to propose a brand.