[RFC] Triangular Workflow UI improvement

> 
> We are working on full implementation of triangular workflow feature.
> For now, the main options available are: 
> 	 - branch.<name>.pushRemote
> 	 - remote.pushDefault
> And only setable by hands. 
> 
> As it can be difficult to understand, here is what we want to do. 
> 
> 
> Context:
> 	- One main remote repository, e.g. git/git.
> 	- A remote fork (e.g. a GitHub fork) of git/git, e.g. me/git.
> 	- A local clone of me/git on the machine
> 
> Purposes:
> 	- the local branch master has to fetch to git/git by default
> 	- the local branch master has to push to me/git by default
> 
> Configuration wanted:
> 	- Add a remote to git/git e.g. `git remote add ...`
> 	- Set the fetch remote for branch as default. 
> 
> For now, we can do that by setting: 
> 	- branch.<name>.remote to git/git
> 	- branch.<name>.pushRemote to me/git
> But many options set `branch.<name>.remote`, a suitable solution is to
> implement an option for the fetch for example. 
> 
> 
> Here is what we want to implement: 
> 
> 1. 
> 	a. add the config var: remote.fetchDefault
> 	b. add the config var: branch.<name>.fetchRemote
> 	c. add `git fetch --set-default` in order to set remote.fetchDefault
> 	d. add `git fetch --set-remote` in order to set branch.<name>.fetchRemote
> 	e. add `git pull --set-default` in order to set remote.fetchDefault
> 	f. add `git pull --set-remote` in order to set branch.<name>.fetchRemote
> 
> 2. 
> 	a. add `git push --set-default` in order to set remote.pushDefault
> 	b. add `git push --set-remote` in order to set branch.<name>.pushRemote
> 
> 
> What's your opinion about this feature ?