`azk start` with remote repository improvement

[marcusgadbem]

When you start an application with remote repository passing a new branch (azk start -o run-project/stringer --git-ref branch-b) and the folder already exists, the script skips cloning the repo and changing branch, joins the folder and start the application with the current active branch. It obviously has a reason: the folder could have uncommited modifications.

So I'd like to suggest an enhacement for this: if we pass a new branch and the folder already exists, we could check if there are uncommited modifications and if there are not, we proceed changing branches (fetching it first if necessary) and starting the application.