Rework data storage

[tomaszdurka]

• Plan is to not rely on the branch name to determine issue which branch is connected with.
• Instead use git config to store github issue name, regardless of the branch name.
• This will allow using branch-feature workflow
• As git branches are related with github pull-requests also base (and possibly head) information should be stored

[tomaszdurka]

Rework following commands

• open
  • creates github issue
  • creates local branch names by issue or title (tbd)
  • checks out issue
  • accepts optional parameter to use certain base
• checkout
  • accepts mandatory parameter issue number
  • checks for local branch connected with that issue
  • checks for remote branch connected with that issue
  • if none exists creates local branch from certain base (optional parameter)
• push
  • pushes code into the base remote's branch
• pull
  • pulls code from base and head (upstream)
  • optional source parameter accepts (head/base) to narrow pull