Emulated EEPROM based on STM32 application note AN3969

Compared to the original implementation from ST, this one:

• is written in C++
• is hardware-independent - flash access is done through StorageAccess interface
• offers significantly faster read/write access to flash memory and page transfers, mainly due to the fact that the contents of entire flash page is stored in RAM
• is unsuitable for devices with low amunt of RAM
• offers ability to specify factory flash page which will get copied to first page when formatting is initiated