Support custom user types (profiles)

UserManagerService recently introduced the notion of user types. This cl
allows customization of those user types:
1. AOSP user types can now be customized
2. New (OEM) user types can be defined

The customization is done via an xml file.
Examples of customization are changing badge icons or changing the
number of allowed profiles per parent. Note that, just because the
values can be set, doesn't mean that the system can actually handle
those values - that must be tested separately.

Currently, only profile types can be customized.

Bug: 142482943
Bug: 142151520
Test: atest UserManagerServiceUserTypeTest
Change-Id: I68011fd3c2f3955e3091a63117a1770a57ecc83b