Implement custom datatypes

Currently when importing from BLF by using a DBC file, all values are doubles. In the DBC file more information about the value can be found:

VAL_TABLE_ Status_value 15 "Invalid" 14 "Reserved" 13 "Reserved" 12 "Reserved" 11 "Reserved" 10 "Reserved" 9 "Reserved" 8 "Reserved" 7 "shutdown" 6 "Sleep" 5 "error" 4 "charge discharge mode" 3 "precharge mode" 2 "ready mode" 1 "Initilization" 0 "Default " ;

It would be nice if those VAL_TABLE_ are imported to labplot and can be easily used as axis labels. It is not neccesary to do it during the import of a BLF file, but maybe also just importing the DBC file

1. Implement importing DBC file:
   • Workbook with a Spreadsheet for every VAL_TABLE_ entry (value, name)
2. Simplify Assigning spreadsheet to axis ticks/labels. Spreadsheet with 2 columns, the first is the value, second the label. So not two steps have to be done.