Account meta data

[JC5]

With the idea of giving accounts more information than just a name, there's a new table and dito coupling for account 'roles', ie. roles for shared accounts, roles for expense accounts, etc. These roles should be expanded in the future to keep track of debet / credit cards, debts and other things.

Since both the name and format of account meta information is completely free-form there should be some kind of documentation / information and maybe some kind of check to see if meta information is valid.

On the other hand, since the account meta fields are currently used for nothing more than 'shared accounts' vs. 'normal accounts', it may be easier to simply drop the whole thing and say shared=1 / shared=0 in one of the account table fields.