Added customfilename option

This is an option to add a custom file name in the options and replace the hard-coded '-blessed'


When used with grunt-bless:

    bless: {
      css: {
        options: {
          'customfilename':'-whatever'
        },
        files: {
          'my-file-ie.css': 'my-file-input.css'
        }
      }
    }


would produce:

my-file-ie.css
my-file-ie-whatever1.css
my-file-ie-whatever2.css

instead of:

my-file-ie.css
my-file-ie-blessed1.css
my-file-ie-blessed2.css


I did not add this to command line options