[WIP] Add Atlassian Bamboo service

# What does this MR do?
Adds support for Atlassian Bamboo as a CI service.

# Are there points in the code the reviewer needs to double check?
I think this will cause a merge conflict with enterprise edition. If so, it will be in the `app/views/projects/services/_form.html.haml` file and is easily resolvable.

I'm also questioning whether we want line 31 changes in `app/views/projects/services/_form.html.haml`. Currently, when EE uses a password for a service it does not utilize this.

# Why was this MR needed?
We want to use Bamboo as a CI service and it was simple to add. I'm certain others would find use, also.

# What are the relevant issue numbers / Feature requests?
None that I'm aware of.

# What's left to do?
I'm still testing this. Also, need to add some docs about how to set things up in Bamboo. It's not super straightforward because Bamboo doesn't have support for webhooks. 
Unused method argument - `data`. If it's necessary, use `_` or `_data` as an argument name to indicate that it won't be used. You can also write as `execute(*)` if you want the method to accept any arguments but don't care about them.