Make the lockscreen adaptive/work in landscape orientation

Currently the lockscreen is portrait-only, meaning if the user selects the landscape orientation, phosh changes the display orientation when locking and unlocking the screen.

This is counter-intuitive and introduces unnecessary complexity in the lockscreen code (need to save current transform, switch to portrait, then re-apply transform when unlocking).

Having the lockscreen work in landscape orientation would require a landscape mode design so it can fit in 360px height (cc @tobias.bernard ), probably by putting blocks side-by-side. A few ideas:

• default view: have the clock/icons block on the left and media-player/notification area on the right
• unlock view: label, input field and "Unlock" button on the left side of the screen, keypad on the right

I'd be willing to work on that if/when we settle on a design.