brat exporter

[joancf]

Create a brat exporter (different from brat writer)
that is thought for representing data

• create the class and arrange the code so the brat writer remains unchanged (or minimal changes)
• change the parameters to allow different improvments:
  • select the feature to represent
  • same color for each feature
  • color depending of a numerical value (between min(clear) /max(darker) )

[joancf]

set new version to 1.9.1-taln