Settings: Add preference for KEY_MIN_REFRESH_RATE

Squashed with the following:

Author: LuK1337 <priv.luk@gmail.com>
Date:   Sun May 9 15:49:43 2021 +0200

    Settings: Remove dependency on pref object for min refresh rate isAvailable()

    Preference is not available during search indexing.

    Change-Id: Ia53aee2a0e4d3c6ef8a56d202af3da48cf6b1d0e

Author: LuK1337 <priv.luk@gmail.com>
Date:   Fri Nov 27 14:33:15 2020 +0100

    Settings: Pass Locale.US when formatting refresh rate string

    * Some locales use comma rather than dot for floating point numbers
      thus causing NumberFormatException when trying to convert string
      to float.
    * Also make sure to strip `,00` too when needed.

    Change-Id: I57d5606858587daf316194c87ece8b5e30423575

Change-Id: Iac1f65ab09717ea55a5b471e094385c77ba894ee