Added ownership to Accounts and Transactions.

[fcomoncho]

Added ownership to Accounts and Transactions, so multiple users can share one Silverstrike instance.

Pending:

• Write tests.
• Add ownership to other models.
• Add ownership functionality to admin views.
• API development to support this change.

[simhnna]

Hi there, thanks for your contribution. However this change would actually break my personal workflow. My wife and I have our own user accounts but access the same data.

I'd prefer if the ownership of the data is based on a group of some sort. In the past I was thinking about creating a new model "Household" that has multiple members and tie all the data to the household and not the actual user. Could also be done with a django group, but with an own model it'd be more flexible going forward

[fcomoncho]

Working on groups and sharing functionality before next PR.