Add the possibility to have multiple vertical Cursors

[siegmund42]

I added the possibility to have multiple vertical Cursors. For this, I adjusted several things:

• Introduce a name for the Cursors that is defined in a separate column vertCursorName of the config file and will be displayed above the frequency text field as well as above the vertical line in the graph
• Make the csv having more than one row. Each row represents a separate cursor. Cursors are dynamically loaded from the config file (max. 20 are possible at the moment - see MAX_NUMBER_OF_VERT_CURSORS). If no config file is present, 4 default cursors are created - see NUMBER_OF_VERT_CURSORS_TO_MAKE.
• Fix enabling/disabling when having multiple markers - did this work beforehand?
• Fix drag&drop when having multiple markers

[pavels]

Cursors is completely reworked including measurements - i am closing this as is it probably not needed anymore (and i can't merge it in current state)