Allow one to specify tags using templates, too.

I'm (hoping to) add this feature so I can accomplish a weird goal of mine --

For JIRA issues, I would much rather have the project name set to 'CMG' (my employer), but include a tag indicating which JIRA project this came from (rather than the project name indicating the JIRA project).  Setting the project name directly is accomplishable using my earlier PR, but creating tags based upon the contents of the issue was previously impossible.

I plan to later add a section to the documentation named something like "Cookbook" to cover how you might configure bugwarrior to handle things like this.

Cheers!