Enhancement: added Areas to S7 PLC Driver implementation

[LucaDazi]

Added a new parameter to the S7 Channel Descriptor, so that information on S7 Area Code can be forwarded to Moka7.

Channel configuration is backward compatible with previous versions.

[nicolatimeus]

It looks like the Counters and Timers areas require special treatment, in this case the value of the Amount argument of ReadArea/WriteArea needs to be adjusted (see Moka7 manual). In this case the library will transfer Amount * 2 bytes, the length of the supplied array must be at least Amount * 2. For the other areas the current implementation should be correct, the library will transfer Amount bytes. I can work on a fix.