Minor change, put default location back into config.h

Move the default location back into config.h to make it easier to find.

Errors and Timestamps

Add a global error code variable called Watchy::err and define values for it in WatchyErrors.h
Make GetLocation, GetWeather, and SyncTime set Watchy::err on failure (or OK on success.) Since
GetLocation and GetWeather always return cached values on errors, there was no other way to tell
if they succeeded or not.
SyncTime no longer returns a value. To check its status check the error code.
Expose the "last successful" timestamp variables for GetLocation, GetWeather, and SyncTime. Each
of those functions store the timestamp of their last successful invocation. It's used internally
for rate limiting, but it can also be used to tell when (or if) they've been successful.

In main.cpp sync the time and set the location if they haven't ever been set.

Bug fix, added documentation, platformio.ini cleanup

Fixed the referent for extern currentTime in Watchy.h

Added a PORTING document that tries to explain how to port a watchface from Watchy to Watchy-Screen

Got rid of the "release" and "debug" environments in platformio.ini that were confusing some people and causing double builds. Now there's just a "debug" build - uncomment the "release" section if you want it.

satisfy extern ref for currentTime

There was an extern for currentTime, but we never defined the referent. Expose currentTime in Watchy, even though it's never updated. Existing watch face code often refers to it to display the time so this makes porting easier.

Fix bug in setting TZ

Bugfix: SetTime and SyncTime weren't setting TZ before using localtime. Move TZ setting into main Watchy so people don't have to remember. Remove TZ setting from TimeScreen.

Add ImageScreen

Added ImageScreen a flavor of IconScreen that displays a vanilla Adafruit GFX bitmap and a label.

Fix bug in time sync

Wasn't setting the default ntpServer name, ever. So time sync would never succeed.

Separate libs for time, location, weather (builds on Linux)

Remove reference to Wifi.h

refactor time, location, weather into libs

Clean up time, location, and weather so that they live in their own libraries. Remove inter-screen dependencies.

Screens have parents

Give screens parents, delete screen names