Accessibility settings refresh.

Categories were added to accessibility service info objects so that they can be grouped
in system Settings. Services can declare a category in their accessibility manifest file,
and if no category is defined, the service is placed under the "Other services" category.

Bug: 30374533

Test: Manually tested with BrailleBack & CTS tests modified to validate proper loading of summary.

Change-Id: I8718556764f2be4a18ce4e80e6bbd4950a41e387