Previously used a monotonically increasing int.  Now uses uuid and nanoseconds.

squashed in:
    [FileEncap11] Read preference from ResearchSettings
    Change-Id: Ic779e0a69db6b16e92c6f4b63dbe7b7add566ab6

    [FileEncap12] Simplify directory cleanup invocation
    Change-Id: I688047409c0343d32b11447fb625dfb726c731ec

    [FileEncap14] Change log filename syntax
    Change-Id: I9243b20b2eb392f81ab8c5c3d19315211240e0bc

Change-Id: I5c9d70e0cb7b0965158e17dd71dfab796bd9a440

- Make ResearchSetting for whether the user has seen the splash screen
- Inline #setLoggingAllowed, which is short and is now only called by
  onUserLoggingConsent

Change-Id: Icdf4592777b80643807b6ccf1d3896459c503e02

- Refer to a common default value in DebugSettings
- Make PREF_USABILITY_STUDY_MODE independent of the ResearchLogger
- ResearchLogger uses its own preference through ResearchSettings

multi-project commit with Ie0df836c9d779eba484b522666ec357f4e234823

Change-Id: I88547a2f619db6e7364abbbec12f9f76855dd11a

Change-Id: I8157249259cf8c3218c5c82a5729f4cbc1fb4eeb