Bangle.js 2 speedups

Hi,

I've been putting a lot of work into Espruino's speed recently, so if you're on (or upgrade to) a cutting edge build (2v15.90 or later) with the latest apps from the app loader hopefully you'll see some big improvements.

• JS speed improvements - I have managed to squeeze around 15% extra performance out of the interpreter since 2v15
  
• Clocks and the Launcher now 'fast switch' (if they both have widgets showing) without reloading the JS environment, which makes things a lot snappier - This is mainly @halemmerich's work
  
• Clock/Launcher loading avoids searching for the correct app each time, shaving ~100ms off the start time
  
• The default launcher now caches app info, which saves a lot of time if you have many apps
  
• Bangle.js now continues to execute JS code while writing to the LCD, which means it can be starting to prepare the next frame while it's sending out the last one
  
• Full-width rectangle fill speed in black/white is now 12x faster
  
• The LCD driver has been completely turned on its head so data is stored in the opposite order and reversed as it is sent out. This makes doing graphics operations around 40% faster
  
  

I'd be really interested to see how you find this... Specifically Clock->Launcher->Scroll->Clock interactions should be hugely improved.

If you encounter issues, please revert back to 2v15 and check they don't exist there - but if you're sure it is something that's broken due to these changes please do let me know in this thread.

... I also added another new clock based on a suggestion from some time ago: https://banglejs.com/apps/?id=slopeclock