Add all informations to the ItemAddress string

[thomas-v2]

For now, we need to address a variable at least the address, e.g. "8A0E000F.11".
Where "8A0E000F" containts of two parts, where 8A0E is for addressing DBs, and 000F is the datablock number (here 15 dec). "11" is thes access id for the variable (also hexadecimal).

To process the read result correctly, we need to know the datatype in the plc, because only with this information we know how to interpret the response data. In the current PlcTag classes, this is done with an additional parameter. For Strings we need further information about the string length.

The idea is to keep all these informations into the access-string. Additional informations are split by a colon ":"
Examples:
"8A0E000F.11:5" is a variable of type Integer
"8A0E000F.11:13.FE" is a variable of type String with a length of 254. If ".xy" is missing, we assume the default length (254).

Could also be done with strings for better readibility:
"8A0E000F.11:Int"
"8A0E000F.11:String.254"