Changing wording on activity; re: #140

Issue #140 describes changes to the wording in the project activity page...I wasn't sure if it was still desired, but I figured I'd work on it since the issue is open.

task.history.mako is used both for the activity tab and also each task. A robust method should continue to detect the location of the list and properly format it in each place. The solution chosen is to create a string variable that is blank if it is called for the individual task, or a link to the task + the task number if it is called for the activity tab. 

This variable is then passed into [mako's filter](http://docs.makotemplates.org/en/latest/filtering.html) in each event's appropriate log statement. With the slight reshuffling of text in the message, I had to alter the translation file for the appropriate strings.

Here's an example of the result for the activity tab: 
![validation](https://cloud.githubusercontent.com/assets/8998918/5429382/c0e0b126-83ae-11e4-9727-f8b13bc57ecb.JPG)

An example of the result for the individual task:
![task](https://cloud.githubusercontent.com/assets/8998918/5429394/f816fbbe-83ae-11e4-9ace-53510e17dc94.JPG)

You'd better use something like:
${_('${user} marked ${task_link} as done', mapping={'user':username, 'tasklink':tasklink)}