Adds an opacity value to the styles defined in the ToolManager.
I set it to 0.5 for fills and 0.8 for strokes so taht we can distinguish
them. I remove some pointless javadoc too without replacing it. I'm not
sure of the behaviour and goal of these methods... So I prefer to let it
empty for now.
Merge pull request #278 from agueganno/tool-opacity

Adds an opacity value to the styles defined in the ToolManager.