Function didn't display negative calibration factors correctly.
Also added option to use the calibration factor without enabling the calibration menu to save some space.
DS1307 does not seem to have the lost lostPower function. So the time does not get set on upload and needs to be set manually as described in the [wiki](https://github.com/sanni/cartreader/wiki/Real%E2%80%90Time-Clock#setting-the-time).
In Config.h set like this:
````
#define RTC_installed
//#define DS3231
#define DS1307
````
Connect "Tiny RTC I2C module" or similar to the SDA/SCL/VCC/GND pins.
Lots of changes/additions.
Added:
* Firmware Updater support: Supports the Firmware Updater app (release to follow soon). Enabled by default, can be disabled in the config.
* 3.3V Fix (3V3FIX): Enable if you have stability issues when using 3.3V, works best with VSELECT. Disabled by default, can be enabled in the config.
* `DynamicClockSerial`: Class that extends and modifies HardwareSerial to be compatible with a dynamically changing clock speed. Used through the `ClockedSerial` object/variable.
* `OSCR.cpp` & `OSCR.h`: New files for storing globals. Only contains these new additions for now. More code cleanup to come.
Changed:
* Moved configuration flags to `Config.h` and documented them better.
* Removed `vselect()` function. Now uses `setVoltage()` with the params `VOLTS_SET_3V3` and `VOLTS_SET_5V`.
Known Issues:
* Rarely the LCD backlight turns white when using 3V3FIX. Resetting fixes it. Doesn't affect functionality/usability; it's just weird.
