Switch type from double to float, switch indexing, change plotting to binary

Speeds up plotting with gnu plot by avoiding intermediate stringstream.

Before (24s for ~24 maps):

[16:48:26:051][  info  ][  scanConsole  ][19201]: -> Storing output results of FE 0
[16:48:26:051][  info  ][    Histo2d    ][19201]: Plotting OccupancyMap-0
...
[16:48:37:951][  info  ][    Histo1d    ][19201]: Plotting OccupancyDist-12
[16:48:37:983][  info  ][  scanConsole  ][19201]: Saving config of FE 0x131bc to configs/0x131bc.json
[16:48:38:362][  info  ][  scanConsole  ][19201]: -> Storing output results of FE 1
[16:48:38:362][  info  ][    Histo2d    ][19201]: Plotting OccupancyMap-0
....
[16:48:49:971][  info  ][    Histo1d    ][19201]: Plotting OccupancyDist-12
[16:48:50:004][  info  ][  scanConsole  ][19201]: Finishing run: 11006

After (6s for ~24maps):

[16:53:47:991][  info  ][  scanConsole  ][21112]: -> Storing output results of FE 0
[16:53:47:991][  info  ][    Histo2d    ][21112]: Plotting OccupancyMap-0
...
[16:53:50:445][  info  ][    Histo1d    ][21112]: Plotting OccupancyDist-12
[16:53:50:479][  info  ][  scanConsole  ][21112]: Saving config of FE 0x131bc to configs/0x131bc.json
[16:53:50:843][  info  ][  scanConsole  ][21112]: -> Storing output results of FE 1
[16:53:50:843][  info  ][    Histo2d    ][21112]: Plotting OccupancyMap-0
...
[16:53:53:181][  info  ][    Histo1d    ][21112]: Plotting OccupancyDist-12
[16:53:53:217][  info  ][  scanConsole  ][21112]: Finishing run: 11007

This is most important for very large maps which will be produced by the thresholdscan.