WIP: Modification for the working of social-help activity.

This PR introduces the changes required in sugar for the functioning of the social-help activity. The changes are self explanatory and I'm adding a few comments (GitHub ones) in the diiff to explain some of the things. 

This PR is a submission to one of the GSoC 2014 sugarlabs projects.

PS: I still have to run pep8 and pyflakes on all files.
The problem with that is this - we need to query this file whenever an activity is launched to determine whether to show the social-help launch button. Clearly, storage on the server is not an option in this case.

The other thing we can do is to show this launch button by default and then, when the button is clicked, we fetch the said json file and check the existence of the activity and launch the proper forum. However, I'll need to show a notification if the activity-category is absent and that's a problem that I wrote about on the mailing list. I need access to a the activity instance to show the notification - this I don't have. So, unless there is a method to display notifications without access to the activity instance, we have a problem.

Or maybe we can store this data in the `.sugar` directory? In that case, updating can be done by simply copying a file to the directory.