* Get rid of the `canToggleGSensor` Device cap, it's now mandatory for `hasGSensor` devices. (This means Kindles can now toggle the gyro, fix#9136).
* This also means that `Device:toggleGSensor` is now implemented by `Generic`.
* Update the Screen & Gyro rotation constants to be clearer (c.f., https://github.com/koreader/koreader-base/pull/1568) (/!\ This might conceivably break some `rotation_map` user-patches).
* Input: Move the platform-specific gyro handling to Device implementations, and let Input only handle a single, custom protocol (`EV_MSC:MSC_GYRO`).
* Input: Refine the `rotation_map` disable method implemented in 43b021d37c. Instead of directly poking at the internal field, use a new method, `disableRotationMap` (/!\ Again, this might break some `rotation_map` user-patches).
* Input: Minor tweaks to event adjust hooks to make them more modular, allowing the Kobo implementation to build and use a single composite hook. API compatibility maintained with wrappers.
* Uses bunch of new plumbing in base to configure screen rotations in hardware (koreader normally does this via blit buffer rotations, except for android).
* Some PB specific kludges that used to pollute core/framebuffer_linux are brought into PBs frontend driver.
* Allow locking the gyro to the current screen mode (i.e., orientation).
* Tweak the "sticky rota" option to work both ways
* More rotation constant usage instead of magic numbers
