- fix use of guid in children classes (need to copy.copy(guid) to avoid clashes)
- move Recurrence to model_common as it is a complex type use by several objects (a.o. Budget and SchedXaction)
- clean model_bugdet (repr, relations, ...)
- redefine guid when need to reference it explicitly in relations (account, budget)
- readonly books block on commit/save and not on flush (so one can still experiment on a RO book) + fix related tests
- check type of datetime
- update repr of account to include commodity mnemonic
- added a "create_stock_from_symbol" based on Yahoo! finance info
- added base_currency to return the base currency if a commodity (book currency for a currency and traded currency for a stock)
- added an "update_prices" to get online quotes for fx rates or stock
- added a "create_stock_accounts" to create default accounts to handle a stock (broker account + income accounts)
- updated commodity and currency link for Price
- create_stock_account only for non currency commidities (raise exception otherwise)
- major refactoring : created a session file for the object, regroup gnucash types into model_common, extracted declarative base into own file, ...