app: Rename MustInit to InitOrDie

Change-Id: a682c99903
git: Prepare for config refactoring

Pulled some functions into a separate package, git/gitutil, because we will need
to break an import circle for the config refactoring in the following commits.

Change-Id: d8ebe787c5
config: Refactor config handling heavily

Change-Id: 5f57ef0f29
Rename msg to task in the whole repository

Started to think that 'task' makes more sense as the variable name for the task
name that is printed to the user when something is run or something fails.

Change-Id: 22b0d4f36c