Show local status by default in stack status command

[geofflamrock]

Background

This PR is part of a series that separates commands that operate on the local Git repository from those that operate against the remote. This is to help align the tool to the way that Git itself operates.

• Show local status by default in stack status command #159
• Adds stack pull command #160
• Adds stack push command #164
• Adds --push option when creating new branches #165
• Adds stack sync command #166
• Changes stack update command to operate on local branches #167

Changes

This PR changes the way that the status command works so that it:

• Reads the status of branches in one go straight from the local repo using git branch -vv rather than lots of calls: This is now so much quicker to the point where can also ditch the Checking status of branches... bit.
• By default doesn't show the status of pull requests, this can now be done with a new option --full.
• Better shows the difference between the remote branch being gone, pr being merged and local branch being gone
• Shows the latest commit sha and message