add raster tools

*** DO NOT MERGE THIS PR
This PR includes the following raster related tools which I created for a project last year. The code is ad-hoc and needs to be improved. Any suggestions are welcome. 
- Raster2Mesh: Converter from Raster ASCII file to Mesh file 
- CSV2Raster: Converter from ParaView CSV file to Raster ASCII file
- addMarginToRaster: add margin to raster data

For Raster2Mesh, I found that the converting function is already existing in current ogs6. so I'll change the main function to use the existing one instead of my ad-hoc code.