change role system

[kateray]

Change the role system so there are 3 possible tax-related roles for Users, for dashboard permissions. The business case here is that trustees shouldn't be able to see what other trustees are pledging (or really, what anyone is pledging on a month-by-month basis) - only the manager of the tax gets to see that.

Currently:
User-level roles:

• Admin
• Trustee

Tax-level roles:

• Manager
• Funder

Desired:
User-level roles:

• Admin (for global access to all the taxes)

Tax-level roles:

• Manager (manages the tax, can do user management like promoting an existing user in the system to a Trustee of that tax)
• Trustee (can see tax dashboard)
• Funder (can only see their own account)

Trustee is a flag on the User, but I think this is wrong and should be removed
Trustee should be a new Role type instead