Sub Menus and Custom Menu Entries

[blueprint]

It would be quite nice to be able to define sub-menus, to better categorise a number of features.

For example, with the sales pack, it would be nice to have the following menu layout:

Home
Support:
- Tickets
- Tasks
Sales:
- Opportunities
- Quotes
- Sales Orders
- Invoices
Reports

Likewise, it would be nice to have some menu entries defined which load filtered subsets of data.

For example, having a "Customers" entry which brings up the "Accounts" list but pre-filtered on "Type" == "Customer"

[blueprint]

Following this, it would be nice to be able to add a "field" to a layout which is pre-filtered.

For example, when using Accounts, we may have "Customer" and "Supplier" types. When creating a new Sales Order, it would nice to only show those Accounts which are of "Supplier" type.